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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

System

Definition

 

ARCO

Stage 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

 Involvement

  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]

Steinberg

Stage 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]