Several different staging systems have been developed and continue to be used. Ficat initially developed an AVN staging system based on radiologic findings. This staging system was revised after the widespread use of MRI in the workup of AVN. The staging system presented in the below table is based on the consensus of the Subcommittee of Nomenclature of the International Association on Bone Circulation and Bone Necrosis (ARCO: Association of Research Circulation Osseous). The most important consideration is collapse of the femoral head cortex. Repair and complete recovery may be possible prior to collapse. Afterward, the collapse is irreversible.

Staging of Avascular Necrosis



Clinical and Laboratory Findings

Stage 0

  • Patient is asymptomatic.
  • Radiography findings are normal.
  • Histology findings demonstrate osteonecrosis.

Stage I

  • Patient may or may not be symptomatic.
  • Radiography and CT scan findings are unremarkable.
  • AVN is considered likely based on MRI and bone scan results (may be subclassified by extent of involvement [see below]).
  • Histology findings are abnormal.

Stage II

  • Patient is symptomatic.
  • Plain radiography findings are abnormal and include osteopenia, osteosclerosis, or cysts.
  • Subchondral radiolucency is absent.
  • MRI findings are diagnostic.

Stage III

  • Patient is symptomatic.
  • Radiographic findings include subchondral lucency (crescent sign) and subchondral collapse.
  • Shape of the femoral head is generally preserved on radiographs and CT scans.
  • Subclassification depends on the extent of crescent, as follows:
    • Stage IIIa: Crescent is less than 15% of the articular surface.
    • Stage IIIb: Crescent is 15-30% of the articular surface.
    • Stage IIIc: Crescent is more than 30% of the articular surface.

Stage IV

  • Flattening or collapse of femoral head is present.
  • Joint space may be irregular.
  • CT scanning is more sensitive than radiography.
  • Subclassification depends on the extent of collapsed surface, as follows:
    • Stage IVa: Less than 15% of surface is collapsed.
    • Stage IVb: Approximately 15-30% of surface is collapsed.
    • Stage IVc: More than 30% of surface is collapsed.

Stage V

  • Radiography findings include narrowing of the joint space, osteoarthritis with sclerosis of acetabulum, and marginal osteophytes.

Stage VI

  • Findings include extensive destruction of the femoral head and joint.