The assessment of acetabular index: is there still a place for plain radiography?

This is a series of 7 children (14 hips) with a mean age of 7.3 years (range, 3.3-10.5 years) and an underlying diagnosis of developmental dysplasia of the hips and no previous open-hip surgery who underwent plain radiographic and magnetic resonance imaging (MRI) measures of bony acetabular index. There was a significant correlation between the measurement of acetabular index using plain radiography and MRI, with a Spearman correlation coefficient of 0.88 (95% confidence interval, 0.61-0.96; P<0.001) and a mean difference between the 2 measures of 0.36+/-6.5 degrees. Furthermore, the bony and cartilaginous acetabular indexes as measured by MRI had a significant correlation with a Spearman correlation coefficient of 0.88 (95% confidence interval, 0.80-0.98; P<0.001). We suggest that plain radiography is still an appropriate tool for follow-up for the nonoperated hip with developmental dysplasia and may be a good indicator of hip cartilaginous development.