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Table 2 Classification systems used in the studies

From: Fibula allograft propping as an effective treatment for early-stage osteonecrosis of the femoral head: a systematic review

ARCOStage 0—bone biopsy positive, all imaging normal
Stage I—normal findings on radiographs and abnormal MRI findings
 IA, < 15%; IB, 15–30%; IC, > 30%
Stage II—abnormal X-ray findings, no femoral head collapse on X-ray and CT, and lesions were subdivided into medial, central, and lateral depending on the location of femoral head involvement
 IA, < 15%; IB, 15–30%; IC, > 30%
Stage III—crescent sign, the lesion can be subdivided into medial, central, and lateral according to the position of femoral head
  IIIA: crescent sign, < 15% or collapse, < 2 mm
  IIIB: crescent sign, 15–30% or collapse, 2–4 mm
  IIIC: crescent sign, > 30% or collapse, > 4 mm
Stage IV—osteoarthritic acetabular changes and cartilage changes
Wei et al. [19], Zeng et al. [20], Wu et al. [21], Feng et al. [23]
SteinbergStage 0—normal or nondiagnostic X-ray, bone scan, and MRI
Stage I—normal X-ray, abnormal bone scan, and/or MRI
Stage II—lucent and sclerotic changes in femoral head
Stage III—subchondral collapse (crescent sign) without flattening
Stage IV—flattening of femoral head
Stage V—joint narrowing and/or acetabular changes
Stage VI—advanced degenerative change
Cao et al. [22]