Table 1.

Chantelau and Richter Charcot classification system (21)

	Grade
Stage	0 (low severity)	1 (high severity)
Active (acute)	Mild edema, erythema, and warmth Possible pain No deformity	Severe edema, erythema, and warmth Possible pain Gross deformity	Clinical
	No osseous abnormality	Macrofractures	Radiographs
	MRI – bone marrow edema, microfractures, no cortical disruption	MRI – bone marrow edema, macrofractures, cortical disruption	MRI
	Lamellar bone with active surface Trabeculae remodeling associated with microfracture Marrow space replaced by loose spindle cells	Increased marrow space vascularity Active remodeling of woven bone Osteonecrosis Invasion of inflammatory cells Thickened synovium Fragmented cartilage and subchondral bone	Histopathology
Inactive (chronic)	No inflammation No deformity	No inflammation Gross deformity	Clinical
	No osseous abnormality	Osseous abnormality	Radiographs
	MRI – no significant bone marrow edema	MRI – no significant bone marrow edema	MRI
	Sclerosis of bone, broad lamellar trabeculae with collagenous replacement; low vascularity of the marrow space	Woven bone, immature and structurally disorganized, fibrosis	Histopathology