Table 5. Bucholz - Ogden classification system of avn of the proximal femur.

Type	Description
I	Irregular ossification of the femoral head with no abnormalities of ossification of the metaphysis is the hallmark of type I AVN.
II	Lateral metaphysis shows evidence of injury; femoral head grows into valgus deformity following premature lateral epiphyseal closure; relative overgrowth of greater trochanter
III	Entire metaphysis affected; femoral neck extremely short, with marked trochanteric overgrowth
IV	Lucent defect along medial metaphysis indicates growth disturbance of medial growth plate, which causes femoral head to grow into varus deformity; relative overgrowth of greater trochanter