Table 2.

ONFH progression to collapse

Stage	Criteria for staging	No. of hips
		At initial visit	At final follow-up
0	Hip at risk with normal X-ray and MRI findings	56	9
I	Abnormal MRI findings, normal X-ray findings	42	1
II	Abnormal X-rays with sclerotic or cystic changes in the femoral head but no crescent line	23	18
III	Abnormal X-rays with a crescent sign and femoral head flattening ≤1 mm	0	0
IV	Collapse of the femoral head ≥1 mm without joint space narrowing	0	2
V	Joint space narrowing	0	49
VI	Advanced degenerative changes	0	42

X-ray indicates plain radiographic imaging. Reprinted from Hernigou et al²¹ with permission.