Composite measurement of scoliosis: a new method of analysis of the deformity.

A method of calculation of biplanar spinal deformity in which the frontal Cobb angle is added to the deviation from normal sagittal alignment is presented. Three equivalent groups of adolescent idiopathic scoliosis treated by different surgical methods are presented. When only the frontal Cobb method of comparison was used, results were similar. When the composite measurement that takes into account sagittal changes was used, the Harrington instrumentation group showed significantly poorer results than the Luque rod and Cotrel-Dubousset rod groups. The composite measurement, considering sagittal alignment, is a significantly more valid method of description of the scoliotic deformity and of comparison of treatment methods.