The Shortcomings of Computer-Aided Measurement of Migration for the Prediction of Failure of Three Forms of Acetabular Fixation by Survival Analysis and Migration Study to Ten Years

We studied, to ten years, migration by vertical displacement and angular change using a digitizer and standard radiographs and survival of three methods of acetabular fixation in primary hip replacement. Two implants were uncemented metal-backed components, one version of which was hydroxyapatite-coated. Both types had 28 mm polyethylene inserts. The third type was a cemented all-polyethylene cup with a 28 mm internal diameter. All cups articulated with a Freeman neck-retaining stem. The purpose was to see if the early migration data predicted the long-term outcome and could be used to forecast implants that would fail for the purpose of pre-market assessment. No statistical differences were found between the groups in the parameters studied. At the threshold accuracies of our migration measurements (three millimetres and three degrees) at three years, we could not identify components that would subsequently fail. However, migration less than these threshold values and the absence of radiolucent lines were strongly associated with implant survival at ten years. Our system was insufficiently accurate for pre-market surveillance.