Measurement of acetabular index intraobserver and interobserver variation

Pelvic radiographs of 25 children aged 6 months to 2 years had the acetabular index measured 3 times by each of five pediatric orthopaedists. Interobserver measurements were found to vary ±3.0°, whereas the intraobserver variation was ± 3.6°. This error reflects only measurement error and does not consider error introduced with different positioning of the pelvis.