Table 1.

Scoring parameters for histological evaluations (modified O’Driscoll score)

Tissue	Parameters	Score
		0	1	2	3	4
Cartilage (Min-Max: 0–31)	Tissue morphology	Fibrous tissue	Mostly fibrocartilage	Mix Hyaline cartilage and fibrocartilage	Mostly hyaline cartilage	Hyaline cartilage
	Matrix staining	None	Slight	Moderate	Normal
	Surface regularity	Disrupted surface	Fissuring	Horizontal lamination of surface	Smooth and intact
	Structure integrity	Severe disintegration	Slight break	Normal
	Neo-cartilage alignment with native cartilage	Depressed	Elevated	Leveled
	Thickness of neo-cartilage	No cartilage	50-100 % of normal cartilage	Similar to normal
	Bonding to the native cartilage	Not bonded	Partially bonded at both ends or bonded at one end	Bonded at the both ends
	Chondrocyte clustering	25-100 % of the cells	<25 % of cells is grouped in clusters	No clusters
	Hypocellularity	Severe	Moderate	Slight	Normal
	Cell distribution	Disorganized	Moderate disorganization	Slight disorganization	Columnar
	Degenerative changes in the adjacent native cartilage	Severe hypocellularity, poor or no staining	Mild or moderate hypocellularity, slight staining	Normal cellularity, mild clusters, moderate staining	Normal cellularity, no clusters, normal staining
	Tidemark continuity	Absent	Partial	Present
Bone (Min-Max: 0–12)	Reconstruction of subchondral bone	No reconstruction	Minimal	Reduced	Normal
	Bone infiltration into defect area	None	Partial	Complete
	Bonding with adjacent bone	Without continuity on either edge	Partial on both edges	Complete on one edge	Complete on both edges
	Subchondral bone morphology	Only fibrous tissue	Compact bone and fibrous tissue	Compact bone	Trabecular with some compact bone	Normal trabecular bone