We assessed whether the range of passive hip motion is reliable for predicting abnormal femoral anteversion. We measured the passive medial and lateral rotation in extension in both hips of 1,140 children between 8 and 9 years of age. The children were divided into 3 groups: group 1: difference between lateral and medial rotation less than 10 degrees; group 2: medial rotation more than 10 degrees greater than the lateral; group 3: lateral rotation more than 10 degrees greater than the medial. Group 1 comprised 90% of the children, whereas 8% belonged to group 2 and 2% to group 3. The angle of femoral neck anteversion was measured in 57 children from the first group, in 67 from the second and in 24 children from the third group, using biplane radiography. The mean anteversion angles in the 3 groups were 24 degrees, 36 degrees and 14 degrees, respectively. To predict an abnormally high anteversion angle (above mean +2SD), the difference between medial and lateral rotation must be 45 degrees or more, whereas an abnormally low anteversion angle (lower than mean -2SD) could be predicted when the lateral rotation was at least 50 degrees higher than the medial rotation.

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