The objective of this study is to investigate whether three dimensional (3D) variability exists within the Lenke classification, and to evaluate the correlations between the 3D features and the Cobb angle used in the Lenke classification. Forty-nine scoliotic patients with Lenke Type 1 curve were selected for analysis. For each patient, the 3D spine model was reconstructed from biplanar radiographs, and the geometric torsion was then calculated from the reconstructed spine model. An analysis of variance (ANOVA) was performed regarding the average torsion, the maximum torsion, and the Cobb angle, with the patients subdivided according to the torsion pattern. Results showed that a statistically significant difference was observed for the torsion parameters (i.e., the average torsion and the maximum torsion) between subgroups within the Lenke Type 1 curves while no statistically significant difference was found regarding the Cobb angle. The strengths of correlations between the torsion parameters and Cobb angle were stronger in the subgroup with torsion pattern of Type A. These results add the evidence that 3D geometric torsion reveals structural differences that are not apparent in the Cobb measurement. © 2013 IEEE.