Idiopathic scoliosis in three dimensions - A succession of two-dimensional deformities?

Study Design. A geometric analysis of computerized three-dimensional (30 reconstructions of the spine of adolescents with idiopathic scoliosis. Objectives. To analyze and describe the 3-D location of scoliotic curves with respect to the global frontal, sagittal, and transverse planes of each subject. Summary of Background Data. Clinical two-dimensional (2-D) measurements cannot fully describe the 3-D deformity of a scoliotic spine because they are done in the 2-D frontal or sagittal plane projection of a subject and do not correspond to the actual deformity. Methods. The spinal deformity from T1 to L5 of 50 adolescents with thoracic idiopathic scoliosis was reconstructed in 3-D using a multiplanar digital radiographic technique allowing the visualization of the vertebral line of the spine in any projection using auto CAD software, The curvature was segmented in three distinct curves for each subject: a high thoracic, a thoracic, and a lumbar. A regional plane passing through the two end-vertebrae and the apical vertebra was defined, and a series of geometric manipulations were performed to realign each regional plane with the global axis system of each subject. Results. A total of 91% of the 147 curves studied were found to be entirely contained within its 2-D regional plane, and all scoliotic curves were found to be oriented in a 3-D location different from the classic frontal, sagittal, and transverse orthogonal planes of each subject. Conclusion. In thoracic idiopathic scoliosis the deformity of the spine is 3-D, but the regional deformity of each high thoracic, thoracic, or lumbar curve is almost always 2-D. The orientation in space of each 2-D plane Is such that it cannot be seen in its true frontal or sagittal projection using standard frontal or sagittal radiologic views of the subject.