|II||+||Osteoporosis, sclerosis, cysts|
|Transition||Flattening and crescent sign|
|III||Collapse||++||Irregular contour of head, sequestrum, normal joint space|
|IV||Osteoarthritis||+++||Flattened femoral head, narrowed joint space; collapse of head (see image)|
Note lucency with well-defined peripheral sclerosis. The frog-leg view is used for assessment of sphericity of the femoral heads. Drawing a circle around the femoral heads on this view will allow for detection of subtle cortical step-offs and early subchondral collapse.