The value of specific radiological features in the classification of acetabular fractures.

Specific radiological features identified by Brandser and Marsh were selected for the analysis of acetabular fractures according to the classification of Letournel and Judet. The method employs a binary approach that requires the observer to allocate each radiological feature to one of two groups. The inter- and intra-observer variances were assessed. The presence of articular displacement, marginal impaction, incongruity, intra-articular fragments and osteochondral injuries to the femoral head were analysed by a similar method. These factors were termed 'modifiers' and are generally considered when planning operative intervention and, critically, they may influence prognosis. Six observers independently assessed 30 sets of plain radiographs and CT scans on two separate occasions, 12 weeks apart. They were asked to determine the presence or absence of specific radiological features. This simple binary approach to classification yields an inter- and intra-observer agreement which ranges from moderate to near-perfect (kappa = 0.49 to 0.88 and kappa = 0.57 to 0.88, respectively). A similar approach to the modifiers yields only slight to fair inter-observer agreement (kappa = 0.20 to 0.34) and slight to moderate intra-observer agreement (kappa = 0 to 0.55).