Osteonecrosis of the femoral head: An update in year 2012

Table 1 Osteoarthritic joint space narrowing with osteophyte formation findings of untreated osteonecrosis

	System
	Ficat/Arlet	Steinberg/U Penn	ARCO
Stage I	Normal radiographs	Normal radiographs	Normal radiographs
Stage II	Subchondral cyst formation and sclerosis	Femoral head lucency/sclerosis	Demarcating sclerosis in femoral head, no collapse
Stage III	Femoral head flattening, subchondral collapse, "crescent sign"	Subchondral collapse without femoral head flattening, "crescent sign"	Femoral head collapse, "crescent sign", no joint space narrowing
IIIA			Collapse < 3 mm
IIIB			Collapse > 3 mm
Stage IV	Osteoarthritic joint space narrowing, degenerative changes	Subchondral collapse, femoral head flattening, normal joint space	Osteoarthritic degenerative changes
Stage V		Flattening with joint space narrowing, acetabular changes, or both
Stage VI		Advanced degenerative changes, secondary osteoarthritis

ARCO: Association Research Circulation Osseous.