Table 1

Radiological stages of ON according to Ficat11

Stage 0This stage is both preclinical and preradiographic. Normal radiograph
Stage 1Standard AP and lateral views are usually normal
Stage 2Changes 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 3The 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 4Progressive loss of articular cartilage and development of acetabular osteophytes