Parameter variation in stable scoliosis.

The reliability of scoliosis parameters such as the Cobb angle, the angle of trunk rotation and moire topography is known from several publications. These studies concern intra- and interobserver variations; they are in general of transversal nature, which means that measurements were performed on the same subject within a short time period. From clinical experience it appears that these variations may be greater when scoliosis patients are followed over several years. In order to determine the parameter variation in the follow-up of children with scoliosis, a retrospective study was undertaken. From among our outpatient population, 41 children with stable scoliosis over a period of at least 2 years were selected. Stable scoliosis was defined as a spinal deformity which, in retrospect, had not deteriorated during at least a 2-year period prior to the end of growth. Hence no indication for treatment was found for this group. The measurements of the angle of external trunk rotation, moire topography and Cobb angle of these children during the follow-up period were submitted to statistical computations using one-way analysis of variance. Variations in the results of Cobb angle measurement and the measurement of the angle of trunk rotation were found to be no different to the variations in intra- and interobserver measurements as reported mainly from transversal studies. The variation found in moire topography, in moire contour lines and in angle moire determination, was, however, considered too great for measurements to be reliable. In conclusion, only Cobb angle determination and external measurement of trunk rotation can be accepted as valid follow-up parameters from a methodological viewpoint.