Accuracy of Ein Bild Röntgen Analyse in determining wear in total hip arthroplasty in vitro

The Ein Bild Röntgen Analyse system is used to radiographically measure femoral head penetration in total hip replacement components. Because determining the accuracy of any wear analysis system is more precise and comparable under in vitro conditions, we used a femoral head migration simulator to assess the accuracy of Ein Bild Röntgen Analyse and determine the effect of magnification factors on accuracy. We used onscreen magnifications of 100% and 200% to measure anteroposterior radiographs, which improved the accuracy of determining femoral head penetration. Improvements averaged 0.056 mm (95% CI +/- 0.013 mm) in the X direction and 0.024 mm (95% CI +/- 0.027 mm) in the Y direction. Femoral head penetration was simulated in 0.25-mm steps from 0-1 mm. Accuracy ranged from 0-0.029 mm (95% CI, 0.035-0.067 mm) for the X direction and from 0.001-0.013 mm (95% CI, 0.046-0.079 mm) for the Y direction. Assuming the worst accuracy combined for the X and Y directions, Ein Bild Röntgen Analyse can accurately detect femoral head penetration greater than 0.128 mm. These results are comparable with reported accuracy values for different systems and suggest that magnification tools should be considered with Ein Bild Röntgen Analyse when measuring wear radiographically.