Here I review the two common classifications for ON of the hip, Ficat and Steinberg.

The modified Ficat, Idiopathic bone necrosis of the femoral head,  was published in 1985 JBJS-Br

0 - Preclinical and pre-radiographic
I - Xray is normal but hip is symptomatic
II - sclerosis and cysts on xray
III - Crescent sign
IV - OA with a deformed head

Steinberg, A quantitative system for staging avascular necrosis, JBJS-Br 1995

0 - Normal
1 - Xray normal, BS +, MRI +
2 - sclerosis and cysts on x-ray
3 - crescent sign
4 - flattening of the femoral head
5 - joint space narrowed without acetabular involvement
6 - advanced DJD

for stages 1 - 5 he further describes volume of involvement
mild <15%
moderate 15% - 30%
severe > 30%

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