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. 2020 Jan 6;21:100–110. doi: 10.1016/j.jot.2019.12.004

Table 2.

The Steinberg - University of Pennsylvania classification of osteonecrosis [61].

Stage 0 Normal or non-diagnostic radiograph, bone scan, and MRI
Stage I Normal radiograph; abnormal bone scan and/or MRI
  • A

    Mild <15% of head affected

  • B

    Moderate 15–30%

  • C

    Severe: >30%
Stage II Lucent and sclerotic changes in femoral head
  • A

    Mild: <15%

  • B

    Moderate: 15–30%

  • C

    Severe: >30%
Stage III Subchondral collapse (crescent sign) without flattening
  • A

    Mild: < 15% of articular surface

  • B

    Moderate: 15–30%

  • C

    Severe: > 30%
Stage IV Flattening of femoral head
  • A

    Mild: <15% of surface and <2 ​mm depression

  • B

    Moderate: 15–30% of surface or 2–4 ​mm depression

  • C

    Severe: >30% of surface or >4 ​mm depression
Stage V Joint narrowing and/or acetabular changes
  • A

    Mild

  • B

    Moderate

  • C

    Severe

Average of femoral head involvement, as determined in stage IV, and estimated acetabular involvement
Stage VI Advanced degenerative changes

MRI = magnetic resonance imaging.