Table 4 Staging of osteonecrosis based on planar radiography, scintigraphy, and magnetic resonance imaging

1

Normal

Increased uptake

Relatively small and well localized, low signal in subchondral zone (T1)

2

Abnormal, cystic and sclerotic changes

Increased uptake

Low signal area subchondral zone diffused down to metaphysis

3

Crescent sign and subchondral collapse producing crescent or rim sign

Increased uptake

Changes with widespread diffusion in metaphysis, surrounded by reactive bone rim,

4

Arthritic changes, joint narrowing with or without condylar involvement

Increased uptake

Diffuse areas of abnormal marrow signal intensity, involvement of the condyle possible