New method for measuring acetabular component positioning with EOS imaging: feasibility study on dry bone

Malposition of the acetabular cup is the most common cause of total hip arthroplasty (THA) dislocation. The position of a total hip implant is usually analysed on computed tomography (CT) scan. We aim to prove it is possible to measure, with good accuracy, the position of an acetabular cup using the low-dose irradiation (EOS) imaging. We implanted an acetabular cup in a pelvic dry bone and measured cup anteversion and inclination with scanography. We performed 14 series of EOS acquisitions with different inclination, rotation and pelvic tilt, which were analysed by five observers. Two observers repeated angle measurements. We then calculated measurement inter- and intrareproducibility and accuracy. Using a confidence interval (CI) of 95 %, inter- and intra-observer reproducibility were +/- 1.6, and +/- 1.4A degrees, respectively, for cup inclination; accuracy in comparison with CT was +/- 2.6A degrees. Using a 95 % CI, inter- and intra-observer reproducibility for cup anteversion were +/- 2.5A degrees and +/- 2.3A degrees, respectively. Measurement accuracy compared with CT was +/- 3.9A degrees. EOS imaging system is superior to standard radiography in terms of measuring acetabular anteversion and inclination.