Ficat and Arlet first classified avascular necrosis of femoral head (AVN) in 1964 before the advent of MRI which was later modified and published in 1985 to include pre-radiographic stages relying on invasive testing procedures. The classification system later underwent further modifications that include MRI findings, patient symptoms and modifies the description of radiographic findings, and excludes the invasive testing procedures originally described.
Mnemonic: All the stages can be remembered with the features starting with the letter ‘S‘.
Stage 0 – Silent hip (Pre-clinical and Pre-radiographic)
Stage I – Suggestive clinically (Pre-radiographic)
Stage IIA – Sclerosis or Subchondral cysts (Pre-collapse)
Stage IIB – Subchondral fracture/crescent sign (Transition)
Stage III – Segemental flattening and Sphericity loss/out of round appearance (Collapse)
Stage IV – Space loss, Secondary osteoarthritis – may involve acetabulum (Advanced arthritis)
MRI is positive in cases of pre-radiographic phases i.e. O and I described in this staging.