Background: The EOS technique represents a unique imaging modality combining low radiation exposure with high image quality. As its applications for pelvic imaging may increase with time, we performed a pilot study to evaluate the validity and reliability of this technique for the assessment of gross pelvic and acetabular morphology.

Methods: Consecutive conventional and EOS radiographs of a human cadaveric pelvis were made in 5° intervals of sagittal tilt and axial rotation (range, -15° to 15° for each). Six measurements were made on each image: (1) the vertical distance between the sacrococcygeal joint and the upper border of the pubic symphysis, (2) the horizontal distance between the midpoints of these structures, (3) the distance between the anterior superior iliac spines, (4) the distance between the facets of S1, (5) the Sharp angle, and (6) the Tönnis angle. Coxa profunda and crossover signs were also evaluated. The findings of the two imaging techniques were correlated with each other and with true linear measurements made on the cadaveric pelvis. All measurements were performed by two independent observers, and one observer repeated all measurements to assess reproducibility. Both observers were blinded to the true linear measurements made on the pelvis.

Results: There was a strong correlation between the results of the conventional and EOS radiography (Pearson correlation coefficient, 0.644 to 0.998), and both modalities had high intraobserver and interobserver reproducibility (intraclass correlation coefficient, 0.795 to 1.000). Intraobserver and interobserver agreement on the presence of coxa profunda were both 100%. Intraobserver agreement (96.2%) and interobserver agreement (92.3%) on the presence of the crossover sign were marginally lower. Linear measurements differed significantly between the two modalities because of distortion caused by magnification effects in the conventional radiographic imaging (p < 0.05).

Conclusions: The EOS imaging technique proved reliable for the assessment of gross pelvic and acetabular morphology, and it may be an alternative to current radiography for primary imaging in the pediatric population and potentially in adults as well. This study did not evaluate the ability of EOS imaging to detect subtle radiographic anatomic abnormalities.