What are the stages of radiographic osteonecrosis?

Steinberg modified Ficat and Arlet stage
Stage 0: normal radiograph, MRI, and bone scan
Stage I: normal radiograph, abnormal bone scan or MRI
Stage II: mottled sclerosis on radiograph
Stage III: subchondral collapse (crescent sign) without flattening of the articular surface
Stage IV: flattening or loss of bone contour without joint space narrowing
Stage V: joint space loss or other manifestations of joint degeneration (i.e., subchondral cysts)
Stage VI: advanced degenerative change