Table 2 Histological degenerative grading according to Bergknut et al. [20]

Morphology of annulus fibrosus (AF)

Chondrocyte metaplasia of AF

Tears and cleft formation

Chondrocyte proliferation of nucleus pulposus

Presence of notochordal cells in nucleus pulposus

0 Well-organized, half ring-shaped, collagen lamellae

1 Mild disorganized; some loss of half ring-shaped structure, most lamellar layer, still distinguishable (<25%)

2 Moderately disorganized; partly ruptured AF, loss of half ring-shaped structure (25–75%)

3 Completely ruptured AF; no or

0 No chondrocyte morphology, just spindle-shaped fibroblasts

1 Mild chondrocyte proliferation (i.e. limited to inner most AF layers)

2 Moderate chondrocyte proliferation (i.e. chondroid cells in up to half of the AF)

3 Marked chondrocyte proliferation (i.e. chondroid cells up to outer layers of the AF)

0 Absent

1 Rarely present

2 Present in intermediate amounts

3 Abundantly present

4 Scar/tissue defects

0 No proliferation

1 Increased chondrocyte-like cell density

2 Connection of two chondrocytes

3 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 defects

0 Abundantly present (>50%)

1 Present (1–50%)

2 Absent

Matrix staining of the nucleus pulposus with Alcian blue/Picrosirius red staining

Endplate morphology

New bone formation

Subchondral bone sclerosis

0 Blue stain dominates

1 Mixture of blue and red staining

2 Red stain dominates

0 Regular thickness; homogeneous structure

1 Slightly irregular thickness

2 Moderately irregular thickness

3 Severely irregular thickness with interruption of the endplate

0 Absent

1 Minor new bone formation

2 Moderate amounts of new bone formation

3 Abundant new bone formation; tendency towards bridging/complete

bridging

0 No sclerosis (<2 _ the thickness of the dorsal vertebral cortex)

1 Mild sclerosis (2–4 _ the thickness of the dorsal vertebral cortex)

2 Moderate sclerosis (>4 _ the thickness of the dorsal vertebral cortex)

3 Severe subchondral bone irregularities