Scheme of ARCO classification system (1992) | ||
Stage | Radiological findings | Subclassification |
0 | Positive: histology. Negative/normal: Radiograph/CT/MRI/Scintigraphy | - |
I | Positive: MRI and/or bone scintigraphy. Negative/normal: radiograph/CT | +’(a) |
II | Radiograph: sclerotic, cystic or osteoporotic changes of femoral head | +’(a) |
III | Radiograph: subchondral fracture (“crescent sign”) | +’(a) |
IV | Radiograph: flattening of femoral head | ++’(b) |
V | Radiograph: flattening of femoral head and osteoarthrotic changes: decreased joint space and acetabular changes | ++’(b) |
VI | Complete joint destruction | - |
(a) Location of femoral head necrosis: 1) medial third, 2) median third, 3) lateral third. Size of femoral head necrosis: A) <15%, B) 15% - 30%, C) >30%. (b) Intrusion degree of femoral head contour: A) <2 mm, B) 2 - 4 mm, C) >4 mm. |