Variability in measurement of acetabular index in normal and dysplastic hips, before and after reduction

This study examined the variability in the measurement of the acetabular in dex (AI) in normal and dysplastic hips, both before and after reduction. Th is variability for dysplastic hips is greater than that of normal hips. The variability is greater before an open or dosed reduction than after reduct ion, and the variability after an open reduction is nearly 3 times greater than after a closed reduction. The 95% confidence interval of the AI is 10. 1 degrees intraobserver and 21.9 degrees interobserver for all hips. The AI is most accurate in the situation in which it is most useful, after a clos ed reduction of a dysplastic hip. A 95% confidence interval of 5.1 degrees in this selected population supports the use of the Al for monitoring aceta bular remodeling after closed reductions in accordance with previous clinic al recommendations.