Analysis of a radiographic assessment method of acetabular cover in developmental dysplasia of the hip.

The aim of this study was to analyse a radiographic assessment method of acetabular cover (Ogata et al.) in developmental dysplasia of the hip (DDH). Intraobserver and interobserver reliabilities of the method were found to be 'substantial' (agreement ratio 85%, kappa coefficient 0.76) and 'moderate' (agreement ratio 71%, kappa coefficient 0.54), respectively. The percentage of hips considered pathological was significantly higher following the use of the acetabular roof shape classification system (15%) than following the measurement of the centre-edge (CE) angle of Wiberg (3%) in the same hips ( p=0.000). The average CE angle of Ogata values of types 1&2, 3 and 4 acetabula were significantly different, whereas the CE angle of Wiberg ones were not. It was concluded that this classification system was a reliable and reproducible radiological indicator for reflecting the acetabular cover. A careful assessment is needed in types 3 and 4 acetabula, because the use of classical angle measurements on plain radiographs such as the CE angle of Wiberg may carry the risk of overestimation of the radiological hip anatomy in such hips.