Study design: The transverse plane evolution of the most common idiopathic deformities was studied using a cross-sectional database of 181 patients whose deformities were visualized by precise three-dimensional techniques.
Objective: The objective was to test the hypothesis that for all common idiopathic scoliosis deformities evolution occurs as a torsion, the apex vertebra translating away from the upper end vertebra and at the same time angulating in a clockwise arc for right apex deformities and a counterclockwise arc for left apex deformities.
Summary of background data: Perdriolle and Vidal proposed this hypothesis in 1987, which explained observations we had made in 1983 and which was partially supported in thoracic curves in our 1992 study.
Methods: Deformities were characterized as single thoracic major, thoracic major and thoracolumbar or lumbar minor, double thoracic and thoracolumbar or lumbar major, and single thoracolumbar or lumbar major curves. The dependent variable studied was the coronal plane regional angular (Cobb) deformity. The independent variables studied were the lateral and anteroposterior translation of the apex vertebra in relation to the upper end vertebra, and the transverse plane translation and angulation of the apex vertebra in relation to the upper end vertebra. For the model or hypothesis to be true, the apex vertebra to upper end vertebra transverse plane translational distance and angular relationship should increase as the Cobb angle increases.
Results: In relation to the upper end vertebra, the apex vertebra always translated laterally, almost always was accompanied by transverse plane translation increase, and usually was accompanied by transverse plane angulation increase. Anteroposterior translation was minimal, but for thoracolumbar and lumbar curves it tended to be posterior.
Conclusion: The theory that these deformities evolve as torsions, with the apex vertebra translating away from the upper end vertebra and at the same time following a clockwise angular pathway to the upper end vertebra of right apex curves and a counterclockwise angular pathway for left apex curves is supported. Compensatory thoracolumbar and lumbar curves evolve in the same manner as major curves.