Table 1 Modified parameters collected for the histologic assessment of disc degeneration and scoring (Boos et al. 2002[31])

cell density (chondrocyte proliferation):

multiple chondrocytes growing in small rounded groups or clusters sharply demarcated by a rim of territorial matrix

0 = no proliferation

1 = increased cell density

2 = connection of two chondrocytes

3 = small size clones (several chondrocytes grouped

together, 3-7 cells)

4 = moderate size clones (8-15 cells)

5 = huge clones (> 15 cells)

structural alterations (tears and clefts):

concentric tears following the collagen fiber bundle orientation in the annulus fibrosus or radiating defects extending from the nucleus pulposus to the outer annulus lamellae parallel or oblique to the end-plate (clefts)

0 = absent

1 = rarely present

2 = present in intermediate amounts between 1 and 3

3 = abundantly present

4 = scar/tissue defects

granular changes:

eosinophilic-staining amorphous granules within the fibrocartilage matrix

0 = absent

1 = rarely present

2 = present in intermediate amounts between 1 and 3

3 = abundantly present

mucous degeneration:

cystic, oval or irregular areas with intense deposition of acid mucopolysaccharides (i.e. sulfated glycosaminoglycans) staining dark blue with Alc-PAS

0 = absent

1 = rarely present

2 = present in intermediate amounts between 1 and 3,

3 = abundantly present

Histologic Degeneration Score (HDS)

0-15 points