Comparison of 3D and 2D characterization of spinal geometry from biplanar X-rays: a large cohort study

Background: Biplanar X-ray system providing anteroposterior and sagittal plane with an ultra-low radiation dose and in weight-bearing position is increasingly used for spine imaging. The original three-dimensional (3D) reconstruction method from biplanar X-rays has been widely used for clinical parameters, however, the main issue is that manual adjustments of the 3D model was quite time-consuming and limited to thoracolumbar spine. A quasi-automated 3D reconstruction method of the spine from cervical vertebra to pelvis was proposed, which proved fast and accurate in 57 patients with adolescent idiopathic scoliosis. The aim of this study was to compare the newly developed technique of quasi-automatic 3D measurement with classical 2D measurements in a large cohort. Methods: A total of 494 adults with biplanar EOS X-ray scanning were included in this study and divided into health and deformity group according to the presence of spinal deformity. The proposed method of quasi-automatic 3D measurement was applied to all these subjects. The radiographic parameters included: thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sagittal vertical axis (SVA), T1 pelvic angle (TPA) in sagittal plane, and cobb angle in coronal plane. Comparison was made between quasi-automatic and manual measurement. Results: The mean age was 53.7 +/- 19.9 years old. In the whole population, the mean differences between the two methods were 3.9 degrees for TK (30.5 degrees +/- 9.9 degrees vs. 26.5 degrees +/- 9.3 degrees, P<0.001), -5.2 degrees for LL (-47.5 degrees +/- 11.2 degrees vs. -42.4 degrees +/- 11.0 degrees, P<0.001), 3.6 degrees for PI (46.9 degrees +/- 10.3 degrees vs. 43.9 degrees +/- 10.3 degrees, P<0.001), -0.2 degrees for PT (11.9 degrees +/- 7.7 degrees vs. 12.0 degrees +/- 8.2 degrees, P=0.328), -2.1 mm for SVA (15.7 +/- 26.2 vs. 17.8 +/- 26.3 mm, P=0.221) and -1.1 degrees for TPA (9.0 degrees +/- 7.6 degrees vs. 10.1 degrees +/- 7.8 degrees, P=0.051). The deformity group had similar mean differences with the asymptomatic group with the values ranged from -4.1 degrees to 3.8 degrees for sagittal parameters. The mean differences of Cobb angle were 1.9 degrees for patients with Cobb angle <30 degrees and 2.3 degrees for patients with Cobb angle >30 degrees, respectively. Correlation analysis showed r2 for all clinical parameters ranged from 0.667 to 0.923. On average, the new method takes 5 minutes to compute all the parameters for one case. Conclusions: In conclusion, this ergonomic and efficient quasi-automatic method for full spine proved fast and accurate measurement in a large population, which showed great potential in extensive clinical application.