Kerboul combined necrotic angles for osteonecrosis

The Kerboul combined necrotic angle is one method used to help predict the risk of osteonecrosis progression to femoral head collapse. The calculation of the combined necrotic angle from magnetic resonance imaging scans combines the angle of necrotic area in the midcoronal image (A) with the angle of necrotic area in the midsagittal image (B). 

The value of the combined angle (A+B) is associated with low, moderate, or high risk of femoral head collapse:

• Low: combined necrotic angle less than 190 degrees
• Moderate: combined necrotic angle between 190 and 240 degrees
• High: combined necrotic angle greater than 240 degrees