Accuracy of EBRA-FCA in the measurement of migration of femoral componentsof total hip replacement

Several methods of measuring the migration of the femoral component after t otal hip replacement have been;described, but they use different reference lines, and have differing accuracies, some unproven. Statistical comparison of different studies is rarely possible. We report a study of the EBRA-FCA method (femoral component analysis using Einzel-Bild-Rontgen-Analyse) to determine its accuracy using three independ ent assessments, including a direct comparison with the results of roentgen stereophotogrammetric analysis (RSA). The accuracy of EBRA-FCA was better than +/-1.5 mm (95% percentile) with a Cronbach's coefficient alpha for interobserver reliability of 0.84; a very good result, The method had a specificity of 100% and a sensitivity of 78% compared with RSA for the detection of migration of over 1 mm. This is accurate enough t o assess the stability of a prosthesis within a relatively limited period. The:best reference line for downward migration is between the greater troch anter and the shoulder of the stem, as confirmed by two experimental analys es and a computer-assisted design.