Table 2.

Osteoarthritis Cartilage Histopathology Grade Assessment.

Grade (Key Feature)	Associated Criteria (Tissue Reaction)
Grade 0: surface intact, cartilage morphology intact	Matrix: normal architecture
	Cells: intact, appropriate orientation
Grade 1: surface intact	Matrix: superficial zone intact, edema, and/or fibrillation (abrasion), focal superficial matrix condensation
	Cells: death, proliferation (clusters), hypertrophy, superficial zone reaction must be more than superficial fibrillation only
Grade 2: surface discontinuity	As above
	+ Matrix discontinuity at superficial zone (deep fibrillation)
	± Cationic stain matrix depletion (safranin O or toluidine blue) upper 1/3 of cartilage
	± Focal perichondronal increased stain (mid zone)
	± Disorientation of chondron columns
Grade 3: vertical fissures	Cells: death, proliferation (clusters), hypertrophy
	As above
	Matrix vertical fissures into mid zone, branched fissures
	± Cationic stain depletion (safranin O or toluidine blue) into lower 2/3 of cartilage (deep zone)
	± New collagen formation (polarized light microscopy, picro sirius red stain)
	Cells: death, regeneration (clusters), hypertrophy, cartilage domains adjacent to fissures
Grade 4: erosion	Cartilage matrix loss: delamination of superficial layer, mid layer cyst formation
	Excavation: matrix loss superficial layer and mid zone
Grade 5: denudation	Surface: sclerotic bone or reparative tissue including fibrocartilage within denuded surface; microfracture with repair limited to bone surface
Grade 6: deformation	Bone remodeling (more than osteophyte formation only); includes microfracture with fibrocartilaginous and osseous repair extending above the previous surface