Table 3.

Chinese staging of osteonecrosis of the femoral head [3].

Stage	Clinical findings	Radiographic signs	Pathological changes
1 (pre-clinical, no-collapse) According to size of necrotic: 1a, small <15% 1b, medium 15%–30% 1c, large >30%	No	MRI Bone scan	Necrosis of bone marrow Necrosis of osteocytes
2 (early stage, no-collapse) According to size of necrotic: 2 a, small <15% 2 b, medium 15%–30% 2 c, large >30%	No or slight pain	MRI X-ray CT	Necrotic area absorbed Bone repair
3 (medium stage, pre-collapse) According to length percentage of crescent in articular facel: 3 a, small <15% 3 b, medium 15%–30% 3 c, large >30%	On set of pain, Slight claudication, Moderate pain, Limited internal rotation, Pain in internal rotation	MRI T2-WI: bone marrow edema, CT: subchondral fracture, X-rays: Femoral head contour interrupted Crescent sign	Subchondral fracture or fracture through necrotic bone
4 (middle–late stage, collapse) According to depth of collapse: 4 a, slight (2 mm) 4 b, medium (2–4 mm) 4 c, severe (4 mm)	Moderate to severe pain, claudication, limited internal rotation, Aggravated pain when strenuous internal rotation, limited abduction and adduction	X-rays: femoral head collapse with normal joint space	Femoral head collapse
5 (late-stage, osteoarthritis)	Severe pain Severe claudication Limited range of motion	X-ray: flattening of femoral head, narrow joint space, acetabular cystic changes or sclerosis	Cartilage involved osteoarthritis