Ultrasound assessment of the acetabulum in the infant hip.

One hundred and fifty infant hips were studied using simultaneous ultrasonography and radiography. The reliability of measurement was found to be similar for alpha angle and d/D ratio. However, the acetabular index correlated much better with the d/D ratio than with the alpha angle. In fact, in hips where the d/D ratio exceeded 56%, radiographs could be dispensed with. Besides, the use of a sector scanner or a linear-array tranducer was found to make no significant difference to the correlation between the acetabular index and the d/D ratio. Sonographic assessment of acetabular development in the infant should permit a reduction in the number of radiographs required during screening and follow-up.