ARCO (Association Research Circulation Osseous) reported a classification of osteonecrosis in 1993. The committee members are from Europe, the United States and Japan.
Patient selection: osteonecrosis of femoral head
Diagnostic modalities:
(1) plain radiographs
(2) scintigraphy
(3) CT
(4) MRI
(5) biopsy with histologic exam
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Diagnostic Modalities
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Stage
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all normal or nondiagnostic
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0
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plain radiograph and CT scan normal; MRI and/or bone scintigraphy abnormal; osteonecrosis in directed biopsy
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1
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femoral head spherical without subchondral fracture (crescent sign absent); imaging studies abnormal (mottling, sclerosis, osteolysis, focal porosis)
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2
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crescent sign visible and femoral head fails mechanically
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3
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progression to osteoarthritis, with narrowing of joint space, acetabular involvement and joint destruction
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4
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Stages 1,2 and 3 are subclassified based on:
(1) location of abnormality: medial, central or lateral
(2) area of femoral head involvement: minimal (< 15%), moderate (15 to 30%). extensive (> 30%)
In Stage 3 there is progressive flattening of the femoral head. Based on the most prominent appearance in plain radiographs the subclassification for extent is based on the maximum of:
(1) area of femoral head involvement with collapse: minimal (< 15%), moderate (15 to 30%). extensive (> 30%)
(2) depression of dome associated with crescent: minimal (< 2 mm), moderate (2 to 4 mm), extensive (> 4 mm)
