Accuracy and reliability of different methods to evaluate the acetabular cup version from plain radiographs

Purpose The purpose of this study was to compare different methods of evaluating the version of a metallic acetabular cup from plain radiographs and to compare them regarding their accuracy, inter- and intra-observer reliability. Methods Conventional anterior posterior radiographs were taken of a phantom-model at different defined ante- and retroversion angles of the acetabular cup. The version angles of the acetabular cup were derived according to four different established methods from the radiographs by five independent examiners. Results We were able to determine the radiographic version with the greatest accuracy according to a modified technique of Pettersson et al. Furthermore, we found the highest intra- and inter-observer reliability using this technique. Conclusions A modified technique of Pettersson et al. broadens the spectrum of applicability for the radiographic evaluation of the version angle of metal-backed acetabular cups in comparison to the originally introduced method. In clinical practice, however, the significance of deriving the cup position from standard radiographs should not be overestimated and therefore a computed tomography should be performed in certain critical cases.