Morphology of annulus fibrosus (AF)0 Well-organized, half ring-shaped, collagen lamellae1 Mild disorganized; some loss of half ring-shaped structure, most lamellarlayer, still distinguishable (75%)Chondrocyte metaplasia of AF0 No chondrocyte morphology, just spindle-shaped fibroblasts1 Mild chondrocyte proliferation (i.e. limited to inner most AF layers)2 Moderate chondrocyte proliferation (i.e. chondroid cells in up to half ofthe AF)3 Marked chondrocyte proliferation (i.e. chondroid cells up to outer layersof the AF)Tears and cleft formation0 Absent1 Rarely present2 Present in intermediate amounts3 Abundantly present4 Scar/tissue defectsChondrocyte proliferation of nucleus pulposus0 No proliferation1 Increased chondrocyte-like cell density2 Connection of two chondrocytes3 Small size clones (i.e., several chondrocytes group together, i.e. 2–7 cells)4 Moderate size clones (i.e. >8 cells)5 Huge clones (i.e. >15 cells)6 Scar/tissue defectsPresence of notochordal cells in nucleus pulposus0 Abundantly present (>50%)1 Present (1–50%)2 AbsentMatrix staining of the nucleus pulposus with Alcian blue/Picrosirius red staining0 Blue stain dominates1 Mixture of blue and red staining2 Red stain dominatesEndplate morphology0 Regular thickness; homogeneous structure1 Slightly irregular thickness2 Moderately irregular thickness3 Severely irregular thickness with interruption of the endplateNew bone formation0 Absent1 Minor new bone formation2 Moderate amounts of new bone formation3 Abundant new bone formation; tendency towards bridging/completebridgingSubchondral bone sclerosis0 No sclerosis (4 the thickness of the dorsal vertebral cortex)3 Severe subchondral bone irregularities