Evidence of three-dimensional variability in scoliotic curves.

In the current study, 98 patients with idiopathic scoliosis were selected for analysis. The object of this study was to determine whether three-dimensional variability exists within each class of the King classification, and to evaluate the currently used King classification in its ability to categorize different scolioses adequately. Anteroposterior and lateral radiographs were digitized, and three-dimensional models were reconstructed for each spine. Several parameters were recorded for each individual: age, gender, four Cobb angles, (1) anteroposterior, (2) lateral, (3) maximum (Cobb angle at the plane of maximum deformity), and (4) minimum (Cobb angle at the plane of minimum deformity), and the orientation of the planes of maximum and minimum deformity. Most of the curves were kyphotic, but a small percentage in each class were hypokyphotic or lordotic. This was not seen in the analysis in which the individual King classes were compared. It was seen, however, when the authors reanalyzed the data after having pooled the subjects and reclassified them according to presence or absence of kyphosis. The King classification was shown to be inadequate for describing spinal deformities in three dimensions, because different variants of sagittal spine configurations were seen which can look identical on the anteroposterior view. Therefore, the need for a new three-dimensional classification, which takes this variability into account, is established.