Anteversion Angle Measurement in Suspected Torsional Malalignment of the Femur in 3-Dimensional EOS vs Computed Tomography-A Validation Study

J Arthroplasty. 2021 Jan;36(1):379-386. doi: 10.1016/j.arth.2020.07.058. Epub 2020 Jul 30.


Background: Computed tomography (CT) scan is the standard for assessment of femoral torsion. This observational study was conducted to evaluate the comparability of the EOS radiation dose scanning system (EOS imaging, Paris, France) and the CT scan in patients with suspected torsional malalignment of the femur.

Methods: Patients with suspected torsional malalignment of the femur were included in a study for surgical planning. The primary endpoint was to compare the 3-dimensional radiological (EOS) imaging system with the CT scan to determine femoral anteversion (AV) angle. Three independent raters performed measurements. Comparability of CT scan and EOS values was assessed by Pearson correlation, t test, interobserver reliability, and intraobserver reliability (Cronbach alpha).

Results: About 34 femora were examined. Interobserver reliability/intraobserver reliability was 0.911 of 0.955 for EOS and 0.934 of 0.934 for CT scan. EOS system revealed an AV angle of 12.2° ± 10.0° (-15.0° to 32.0°). CT examinations showed an AV angle of 12.6° ± 9.2° (-3.2° to 35.6°). About 11 hips featured physiological AV, 14 hips showed decreased AV (<10°) or retroversion (<0°), and 9 hips showed increased AV (>20°). Overall, a strong Pearson correlation of τ = 0.855 and a highly significant correlation in the t test for both methods was seen. In patients with decreased AV, retroversion, or increased AV, Pearson correlation only resulted in a moderate/low correlation of τ = 0.495 and τ = 0.292. The t test showed no significant correlation at malrotation.

Conclusion: In torsional malalignment, EOS does not have correlation with CT measurements. In contrast to CT scan, EOS allows femoral torsion measurement independent of legs' positioning.

Keywords: CT scan; EOS; measurement of rotation; reliability; rotational alignment femur; torsional malalignment hip.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Femur* / diagnostic imaging
  • France
  • Humans
  • Physical Examination
  • Reproducibility of Results
  • Tomography, X-Ray Computed*