Femoral anteversion in infants: a method using ultrasound.

OBJECTIVE

To design a reproducible method to measure femoral anteversion in children under 1 year old.

DESIGN AND PATIENTS

We conducted a prospective, observational study to determine intra- and inter-observer reproducibility of the sonographic measurement of femoral anteversion in infants. The method involves imaging of the proximal femur using a vertical transducer with the infant in the lateral position. Anterior femoral anteversion is measured using a vertical baseline and a line tangential to the anterior femoral head and the trochanter (anterior anteversion). We similarly measured true femoral anteversion using a line passing through the centre of the femoral head and the femoral neck (true anteversion). Anteversion measurements were taken at the time of routine ultrasound screening for developmental dysplasia of the hip when infants were an average of 10.4 weeks old. Anteversion measurements were made in 74 hips (37 infants).

RESULTS

Our results showed that for the anterior anteversion measurements intra-observer repeatability was +/-6.2 degrees and inter-observer repeatability was +/-7.8 degrees. For true anteversion measurements intra-observer repeatability was +/-9.5 degrees, but inter-observer repeatability was +/-23.5 degrees.

CONCLUSIONS

Our results have shown that our method for measuring "anterior femoral anteversion" has an acceptable level of inter- and intra-observer agreement. The method used to determine "true anteversion", however, proved to have an unacceptable level of inter-observer variability.