A comparison of the reliability and vulnerability of 3D sterEOS and 2D EOS when measuring the sagittal spinal alignment of patients with adolescent idiopathic scoliosis

Purpose An essential component of making the diagnosis of adolescent idiopathic scoliosis (AIS) is standing anteroposterior and lateral radiographs. Two-dimensional (2D) radiographs inevitably fail to reflect every plane of the three-dimensional (3D) deformity in scoliosis. We have tested the hypothesis that there is no difference in the assessment of the sagittal plane deformity when measured with either 2D or 3D EOS radiography. Methods A retrospective radiographic analysis was performed on patients diagnosed with AIS, with subdivided into three groups according to the coronal angular deformity (mild group: 45°–69°, moderate group: 70°–89°, and severe group: 90° +). The sagittal parameters were compared between manual measurement with 2D sterEOS and those made using computer-aided 3D reconstruction. Results Fifty-two patients were included in each group. The inter-study reliability when measuring the thoracic Kyphosis (TK) and lumbar lordosis (LL) between the two study modalities was excellent in mild group (ICC: 0.90, 95% CI 0.82 ~ 0.94 and ICC: 0.84, 95% CI 0.74 ~ 0.91), excellent in TK and fair in LL in moderate group (ICC: 0.76, 95% CI 0.61 ~ 0.85 and ICC: 0.70, 95% CI 0.53 ~ 0.81), and fair in TK and LL in severe group, respectively (ICC: 0.74, 95% CI 0.57 ~ 0.84 and ICC: 0.65, 95% CI 0.46 ~ 0.84). A Bland–Altman plot showed proportional bias in TK measurements in each group and LL in moderate group, which means the measured value is underestimated in 2D method when the angle is small. Conclusion 3D sterEOS is less vulnerable to the influence of coronal plane than 2D EOS in evaluating the sagittal spinal parameters of patients with a coronal deformity exceeding 70°. Level of evidence 4.