There are a number of classification systems for intracapsular fractures of the proximal femur, but none has been shown to be practical with satisfactory reproducibility and accurate predictive value. We have investigated the AO classification and evaluated intra-and interobserver accuracy and its value in predicting treatment and outcome.

We found it to have very poor intra- and interobserver reliability and to be of limited predictive use for the outcome of treatment. A simplified system in which the subdivisions were allocated to one of three groups of undisplaced, displaced and basal fractures was found to be of value. We conclude that this is the only division which is appropriate for these fractures and that the AO system for intracapsular fractures is too complicated and should not be used.