Table 5. Correlation of MRI features (ARCO staging system) and combined plain X-ray + MRI features (Ficat and Arlet classification).

AVN, avascular necrosis; ARCO, Association Research Circulation Osseous; MRI, magnetic resonance imaging

Stages of AVN of the hip	Percentage (%) and number of hips (n)
	ARCO staging system	Ficat and Arlet classification
Stage I	4.4% (n = 2)	4.4% (n = 2)
Stage II	28.9% (n = 13)	28.9% (n = 13)
Stage III, early (flattening of the femoral head)	Early IIIA, 4.4% (n = 2)	51.1% (n = 23)
	Early IIIB, 8.9% (n = 4)
	Early IIIC, 13.3% (n = 6)
Stage III, late (flattening with eventual femoral head collapse)	Late IIIA, 4.4% (n = 2)
	Late IIIB, 13.3% (n = 6)
	Late IIIC, 6.7% (n = 3)
Stage IV	15.6% (n = 7)	15.6% (n = 7)