Index of Necrotic Extent for Osteonecrosis of the Femoral Head

Description

Koo and Kim developed the index of necrotic extent (alternatively called the index of necrosis) for a patient with osteonecrosis of the femoral head. This can help classify patients according to the amount of osteonecrosis present. The authors are from the Gyeong-Sang National University School of Medicine in Chinju, South Korea.

Method:

(1) Perform MRI of the affected femoral head with images in the coronal and sagittal planes.

(2) Identify the center of the femoral head in the selected image, assuming a circle.

(3) Define the arc between the two edges of the infarct along the articular surface of the weight-bearing portion, with the angle of interest at the center of femoral head.

Parameters:

(1) arc of necrotic tissue in the mid-coronal image in degrees from 0 to 180

(2) arc of necrotic tissue in the mid-sagittal image in degrees from 0 to 180

index of necrotic extent =

= (arc in mid-coronal image) / 180 * (arc in mid-sagittal image) / 180 * 100

Interpretation:

• minimum index: 0

• maximum index: 100

• The index shows a strong correlation with the risk of collapse.

Index	Size	Grade
<= 33	small	A
34 to 66	medium	B
>= 67	large	C

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Index of Necrotic Extent for Osteonecrosis of the Femoral Head

Description

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