Ultrasonography of the hip in preterm neonates.

Over the period of one year, the hips of 92 preterm neonates were examined by ultrasound. Using the Graf classification only 7% showed an angle alpha between 50 and 60 degrees, which is characteristic of type IIa hips. In all other cases the angle alpha was above 60 degrees (type I). Sonographically there were no pathological cases (type IIg or worse). A reason for the relatively low number of type IIa hips could be that the short osseous acetabular rim and the broad cartilagenous Y-joint in this age group result in a "false" increase of the angle alpha.