Lateral center-edge angle
The lateral center-edge angle is a radiographic measurement of femoral head bony coverage by the acetabulum. It has since been shown superior to the extrusion index in measuring femoral head undercoverage.
Usage
It has primarily been described in assessing for acetabular dysplasia, but can also be used in femoroacetabular impingement.
Measurement
This angle is calculated on AP pelvic radiographs by drawing a best fit circle for the inferior and medial margins femoral head. The angle is then measured between two lines drawn from the center of the circle, one running vertically along the longitudinal axis of the pelvis and the other to the lateral acetabular rim.
In the modification by Ogata the second line runs to the lateral edge of the acetabular sourcil .
Interpretation
Values between 25° and 39° are considered within the normal range .
As expected, lateral bony rim and acetabular sourcil measurements show significant differences, which needs to be taken into account .
Increased lateral center-edge angle
- >39°: pincer type impingement
Reduced lateral center-edge angle
- <20°: acetabular dysplasia (i.e. developmental dysplasia of the hip)
- between 20° and 25°: borderline acetabular dysplasia
Pitfalls
- cannot be measured in patients with abnormal femoral heads due to previous injury or avascular necrosis
History and etymology
It was originally described by Wiberg in 1939 .
