EOS imaging and scoliosis: the clinical applicability and intra-rater repeatability of measures

Objectives

EOS bi-planar imaging enables three-dimensional (3D) reconstructions of the spine and pelvis with segmental vertebral measurements in three planes from a neutral pelvis. This study evaluates the repeatability of these measurements and the accuracy in detecting true changes.

Methods

Twenty patients from four clinical backgrounds (surgical threshold, bracing threshold, micro-dose, and in-brace) were included. EOS bi-planar “full spine” images were modelled and then subsequently re-modelled at least 4 weeks later by the same researcher. All 3D measurements were recorded and compared.

Results

The average modelling interval was 6.7 weeks. Paired measures indicated high agreement, except for planes of maximal curvature (PMC): thoracic (Spearman’s = 0.67; p < 0.05) and lumbar (Spearman’s = 0.40; p > 0.05). Intraclass correlation coefficients (ICCs) showed excellent agreement, with thoracic and lumbar Cobb angles averaging 0.99. Sagittal measurements ranged from 0.93 (L1/S1 lordosis) to 0.96 (T1/T12 kyphosis). Pelvic parameters ranged from 0.88 (obliquity) to 0.99 (tilt). The transverse profile ranged from 0.82 (apical thoracic rotation) to 0.98 (average lumbar rotation). Repeatability (2.77 × technical error of measurement [TEM]) was ± 4.4° for Cobb angles, ± 7.7° for sagittal profile, ± 5.0° for pelvic parameters, ± 4.8° for transverse profile, and ± 100.4° for automated thoracic and lumbar PMC. With strong outliers excluded, thoracic PMC was ± 16.2° and lumbar PMC was ± 15.5°.

Conclusion

3D EOS measurements demonstrate excellent intra-rater ICC repeatability despite notable true measurement error that should define future success criteria. Semi-automated modelling provides quick 3D spinal alignment measurements from a neutral pelvis, with this study being the first to report TEM for 3D EOS reconstructions. PMC disagreement indicates the need for further investigation.