Table 1 Staging of osteonecrosis based on planar radiography and magnetic resonance imaging (MRI) according to Carpintero [16], Lotke [6], and the modified Ficat and Arlet classification [5, 9]
Stage | Radiography | MRI |
|---|---|---|
1 | Normal | Relatively small and well localized, low signal in subchondral zone (T1) |
2 | Abnormal, cystic, and sclerotic changes | Low signal area in subchondral zone diffused down to metaphysis |
3 | Crescent sign and subchondral collapse producing crescent or rim sign | Changes with widespread diffusion in metaphysis, surrounded by reactive bone rim |
4 | Arthritic changes joint narrowing with or without condylar involvement | Diffuse areas of abnormal marrow signal intensity, involvement of the condyle possible |