Table 1 Classification of avascular osteonecrosis (AVN) as performed by the Association Research Circulation Osseous (ARCO). Diagnostic findings, localisation and extent of AVN are considered. AVN-associated pain usually occurs in late ARCO stages III and IV but can also be found in earlier stages. BME = bone marrow oedema; nps = no pathological signs [27–30]
From: Rationale for prostaglandin I2in bone marrow oedema – from theory to application
ARCO stages | |||||
|---|---|---|---|---|---|
0 | I | II | III | IV | |
Diagnostic techniques and findings X-ray | nps | nps | Sclerosis, osteolysis, focal osteoporosis | Crescent sign, flattening of the articular surface (subchondral fracture) | Collapse, joint space narrowing (osteoarthritis) |
CT | nps | nps | Asterix sign, sclerosis | Subchondral fracture | Collapse, joint space narrowing (osteoarthritis) |
Bone scan | nps | Cold spot | Cold in hot spot | Hot in hot spot | Hot spot |
MRI | nps | BME | Osteonecrosis, reactive interface | Subchondral fracture | Collapse, joint space narrowing (osteoarthritis) |
Subclassification | No | - medial | No | ||
- central | |||||
- lateral | |||||
Quantification | No | % area involvement: | Length of crescent: | % of surface collapse and dome depression | No |
Minimal A: <15% | A: <15% | (A, B, C) | |||
Moderate B: 15 to 30% | B: 15 to 30% | ||||
Extensive C: >30% | C: >30% | ||||