Radiological stages of ON according to Ficat11
| Stages | Description |
|---|---|
| Stage 0 | This stage is both preclinical and preradiographic. Normal radiograph |
| Stage 1 | Standard AP and lateral views are usually normal |
| Stage 2 | Changes in the trabecular pattern of the femoral head: |
| sclerosis diffuse in localised areas or in a linear arc that is concave superiorly | |
| decalcification generalised or in the form of small cysts in the head | |
| mixed form including both sclerosis and cysts | |
| Stage 3 | The pathognomonic appearance of the sequestrum preceded by: |
| crescentic line caused by subchondral fracture | |
| segmental flattening of the femoral head: the so called “out of round” appearance | |
| Stage 4 | Progressive loss of articular cartilage and development of acetabular osteophytes |