TABLE 1.

Osteoarthritis Research Society International (OARSI) Grading System

Grade	Subgrade	Associated Criteria
0: Surface intact, cartilage intact	None	Intact, uninvolved cartilage
1: Surface intact	1.0: Cells intact 1.5: Cell death	Matrix: superficial zone intact, edema and/or fibrillation Cells: proliferation (clusters), hypertrophy Reaction must be more than fibrillation only
2: Surface discontinuity	2.0: Fibrillation through superficial zone 2.5: Surface abrasion with matrix loss within superficial zone	Features for grade 1: + discontinuity at superficial zone, ± safranin O or toluidine blue depletion on upper one-third of cartilage (mid zone), ± chondron column disorientation
3: Vertical fissures	3.0: Simple fissures 3.5: Branched/complex fissures	Features for grade 2: ± safranin O or toluidine blue on upper two-thirds of cartilage (deep zone), ± neocartilage formation (polarized light microscopy, picrosirius red stain)
4: Erosion	4.0: Superficial zone delamination 4.5: Midzone excavation	Cartilage matrix loss, cyst formation within matrix
5: Denudation	5.0: Bone surface intact 5.5: Reparative tissue surface present	Surface is sclerotic bone or reparative tissue including fibrocartilage
6: Deformation	6.0: Joint margin osteophytes 6.5: Joint margin central osteophyte	Bone remodeling; deformation of articular surface contour (more than osteophyte formation only); includes microfracture and repair