Evaluation of a Three-Dimensional Reconstruction Method of the Rib Cage of Mild Scoliotic Patients

Study DesignValidation study.ObjectiveTo evaluate a method of 3-dimensional (3D) reconstruction of the rib cage in a population of scoliotic patients.Summary of Background DataEvaluation of the thoracic cage clinical parameters would be helpful in the management of spinal deformities.MethodsBiplanar X-rays were performed using the EOS system and the rib cage was reconstructed using a previously developed semi-automated method. Thoracic parameters were calculated from the 3D reconstructions: volume, frontal and sagittal diameters, 3D spinal penetration index (SPI), thoracic index, and rib hump. To test accuracy, the authors constructed biplanar projections from 3 computed tomography scans and then used these projected X-rays as material for stereoradiographic reconstructions. The models were then compared with volumetric objects reconstructed from these 3 computed tomography scans. To test intra-observer and interobserver reproducibility, 22 chests (mean Cobb angle, 28° [range, 17° to 45°]) were reconstructed twice by 3 operators. The 95% confidence interval was calculated for the study parameters.ResultsThe mean signed point to surface distance was −1.6 mm. Interobserver reproducibility was 9 mm for maximum anteroposterior and lateral diameters, <0.8% for SPI, 5° for rib hump, .02 for thoracic index, and 450 cm3 for volume.ConclusionsThe results of the reproducibility study were satisfactory. The 95% confidence interval was <6% for the transverse diameters and <10% for volume and SPI. The reported method of 3D reconstruction of the rib cage provides accurate and reproducible determinations of the investigated thoracic parameters in scoliotic patients.