Table 1.

Association Research Circulation Osseous classification of osteonecrosis [14, 15]

Stage	Findings	Subclassification	Quantitation
0	All present techniques normal	No	No
I	Radiography and computed tomography normal; at least one of the other techniques is positive	Location of lesion Medial Central Lateral	Area of involvement (%) A: < 15% B: 15 to 30% C: > 30% Length of crescent A: < 15% B: 15% to 30% C: > 30% Surface collapse and dome depression A: < 15% and < 2 mm B: 15% to 30% and 2 mm to 4 mm C: > 30% and > 4 mm
II	No crescent sign; Sclerosis, osteolysis, focal porosis
III	Crescent sign and/or flattening of articular surface
IV	Osteoarthritis, joint space narrowing, acetabular changes, joint destruction	No	No