Table 1 Microscopic grading system for articular cartilage histology [8]

Chondrocyte necrosis*

0

Normal section without necrosis

1

No more than one necrotic cell located near the articular surface per 20x objective

2

1e2 necrotic cells located near the articular surface per 20x objective

3

2e3 necrotic cells located near the articular surface per 20x objective

4

3e4 necrotic cells located near the articular surface per 20x objective

Cluster (complex chondrone) formation

0

No cluster formation throughout section

1

Two chondrocytes (doublets) within same lacunae along superficial aspect of the articular cartilage section

2

2e3 chondrocytes (doublets & triplets) within same lacunae along superficial aspect of the articular cartilage section

3

3e4 chondrocytes within same lacunae along superficial aspect of the articular cartilage section

4

Greater than four chondrocytes within same lacunae along superficial aspect of the articular cartilage section

Fibrillation/fissuring

0

No fibrillation/fissuring of the articular cartilage surface

1

Fibrillation/fissuring of the articular cartilage restricted to surface and superficial zone

2

Fissuring that extends into the middle zone

3

Fissuring that extends to the level of the deep zone

4

Fissuring that extends into the deep zone

Focal cell loss*

0

Normal cell population throughout the section

1

A 10e20% area of acellularity per 20x field

2

A 20e30% area of acellularity per 20x field

3

A 40e50% area of acellularity per 20x field

4

A greater than 50 % area of acellularity per 20x field

Safranin-O stain uptake

0

Normal staining

1

Less than 25 % loss of staining characteristics

2

25e50% loss of staining characteristics

3

50e75% loss of staining characteristics

4

Greater than 75 % loss of staining characteristics