Reliability of Acetabular Measures in Developmental Dysplasia of the Hip

The purpose of this study was to determine the reliability in the measurement of the acetabular index
and the acetabular angle in children with developmental dysplasia of the hip. Seventeen children with
unilateral developmental dislocation of the hip treated by closed reduction were reviewed. The acetabular
index and the acetabular angle of 34 hips were measured twice by two observers. The method of Bland
and Altman as outlined by Loder was used to calculate reliability. Mean age at reduction was 9 months.
Radiographs were reviewed at a mean of 58 months following reduction. The intraobserver reliability
of the acetabular index in involved hips was š4.1°. The intraobserver reliability of the acetabular angle
for involved hips was š3.6°. The interobserver reliability of the acetabular index in involved hips was
š13.7°. The interobserver reliability of the acetabular angle for involved hips was š7.8°. To ensure true
change, a single observer should document at least an 8° change in the acetabular index or a 7° change
in acetabular angle between two radiographs. (Journal of Surgical Orthopaedic Advances 14(2):73–76,
2005)
Key words: acetabular angle, acetabular dysplasia, acetabular index, developmental dysplasia of the
hip, interobserver/intraobserver reliability