The literature has recently underlined the interest of pelvic and acetabular component orientation measurements in the standing and sitting position. Radiographic follow-up of total hip arthroplasty (THA) is based on standard AP and lateral X-rays. The use of EOS™ 2D imaging system reduces patient’s radiation exposure compared to conventional X-rays. However, using this system, the validity and reproducibility of angular measurements, have not been studied yet for the measurement of pelvic and acetabular parameters in patients with THA.

The EOS™ 2D imaging system offers similar advantages to conventional X-rays in the measurement of pelvic and acetabular orientation parameters which are commonly used.

Five angular parameters characterizing pelvic tilt and acetabular cup orientation were determined using the same digital measurement Imagika™ software based on two series of standard X-rays and EOS™ 2D images acquired in both standing and sitting positions. Radiographs from 50 patients with unilateral THA were measured three times by two observers. Intra- and interobserver reproducibility using each method was independently studied then paired comparison was performed.

The ICC and Spearman rank correlation coefficient demonstrated an excellent EOS/conventional X-ray correlation. According to the parameters, the mean difference between these two imaging modalities ranged from 0.30° to 3.43° (P<0.05). The intra- and interobserver variability ranged from±2.97° to±6.46° using the EOS™ imaging system and from±4.26° to±10.22° using conventional X-rays (P<0.05).

The EOS™ 2D imaging system may replace conventional X-rays in the assessment and monitoring of pelvic and acetabular cup orientation in THA.

Level III. Prospective diagnostic study.