Pelvis and total hip arthroplasty acetabular component orientations in sitting and standing positions: Measurements reproductibility with EOS imaging system versus conventional radiographies

Introduction: 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 (TM) 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. Hypothesis: The EOS (TM) 2D imaging system offers similar advantages to conventional X-rays in the measurement of pelvic and acetabular orientation parameters which are commonly used. Patients and method: Five angular parameters characterizing pelvic tilt and acetabular cup orientation were determined using the same digital measurement Imagika (TM) software based on two series of standard X-rays and EOS (TM) 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. Results: 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 degrees to 3.43.degrees (P < 0.05). The intra-and interobserver variability ranged from +/- 2.97 degrees to +/- 6.46 degrees using the EOS (TM) imaging system and from +/- 4.26.degrees to +/- 10.22 degrees using conventional X-rays (P < 0.05). Discussion: The EOS (TM) 2D imaging system may replace conventional X-rays in the assessment and monitoring of pelvic and acetabular cup orientation in THA. Level of evidence: Level III. Prospective diagnostic study. (C) 2011 Elsevier Masson SAS. All rights reserved.