Patient selection: The center of the femoral head shows a large variation in infants and young children. It is more reliable in patients >= 5 years.
Imaging studies: anteroposterior (AP) radiograph of the pelvis with the patient supine and the legs in a neutral position.
The critical factor is an accurate determination for the center of the femoral head. Normally this is found easily along the epiphyseal line. If the femoral head is distorted, then the center can be located using a template of concentric circles (Mose, 1964) or an ischiometer (Muller, 1955)
Lines to draw on the radiograph:
(1) vertical line from the center of the femoral head, perpendicular to Hilgenreiner's line (through both triradiate cartilages of the hips = through the inferior boney margins of the ilia at the point of origin of the acetabular roof) and parallel to the longitudinal body axis
(2) line from the center of the femoral head to lateral edge of the acetabular roof
The CE angle is the angle between these 2 lines at the center of the femoral head.
The angle is positive if the line to the acetabular edge is lateral to the vertical line, and negative if it is medial.
Interpretation:
• A large, positive angle indicates a deep acetabulum.
• A small or negative angle is seen with subluxation of the femoral head
|
Age
|
Normal Mean Angle
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Abnormal if
|
|
5 to 8
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25°
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< 20°
|
|
9 to 12
|
30°
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< 25°
|
|
13 or older
|
35°
|
< 25°
|
from Tonnis, page 121
