Acetabular Cartilaginous Angle A New Method for Predicting Acetabular Development in Developmental Dysplasia of the Hip in Children Between 2 and 18 Months of Age

Background: A new method of arthrographic measurement, the acetabular cartilaginous angle (ACA), is described here in an effort to find a simple, reliable, and reproducible measurement that can predict future acetabular development after successful closed reduction of developmental dysplasia of the hip (DDH). Methods: A prospective study was conducted for children with DDH who were treated successfully by closed reduction in the authors' institute from 1994 through 2000. The total number of patients who completed the follow-up in our study until full acetabular development or acetabuloplasty was 162, with 234 affected hips. Their age at the time of closed reduction ranged between 2 and 18 months (mean, 7.48 months; SD +/- 5.162). There were 135 girls and 27 boys. Frank dislocation of the hip was present in 195 hips, whereas acetabular dysplasia with or without lateralization of the femoral head was seen in 39 hips. The average follow-up was 9.2 years (range, 6-11 years). Results: Multivariate analysis of 6 variables showed that the mean age and acetabular index at the time of closed reduction were significant to predict later acetabuloplasty, whereas ACA was highly significant. These 3 significant variables together had 96.58% correct prediction. The authors observed that some hips with high acetabular index developed satisfactorily, and other hips with small values required later acetabuloplasties. On the other hand, there was a clear cut value of ACA (20 degrees) under which almost all hips (99.5%) developed satisfactorily and another clear cut value of ACA (24 degrees) above which all hips (100%) needed acetabuloplasty. Conclusions: Acetabular cartilaginous angle is considered a reliable measurement to identify hips with DDH that will need later acetabuloplasty after successful closed reduction. The acetabular index is important in monitoring acetabular development, and reaching a value of less than 30 degrees 2 years after closed reduction is considered a good sign of acetabular development. Level of Evidence: Prognostic study of Level I.