Introduction: In this study we focus on idiopathic scoliosis with a primary thoracic curve and a secondary lumbar curve. We were interested in how the lumbar curve corrects following selective thoracic fusion and whether one can predict the correction of the lumbar curve. In the literature it is said that the lumbar curve spontaneously corrects to balance the thoracic curve after selective thoracic fusion. Because of these findings we postulate there should be a correlation between the correction of the lumbar and thoracic curve of the scoliosis.

Recently we showed in patients treated with Harrington instrumentation with sublaminar wiring (second generation technique) that the correction of the lumbar curve was not a reflection of the thoracic correction. So it is interesting to know whether with the use of third generation instrumentation techniques and more sophisticated classification systems the correlation of the unfused lumbar cure becomes more predictable.

Objective: To establish whether in primary thoracic idiopathic scoliosis treated with selective thoracic fusion using CD instrumentation there is a significant correlation (p< 0.05) between the correction of the thoracic and lumbar curve. And to assess whether, in the in the individual patient, the lumbar modifier (A, B and C) according Lenke, can be used as a correct predictor of outcome results. The higher the correlation coefficient between the relative (%) corrections of the thoracic and lumbar curves, the higher the predictability of the correction of the unfused lumbar curve.

Material and methods: We performed a retrospective study on 38 patients with adolescent idiopathic scoliosis treated by selective thoracic fusion (CD instrumentation). There were 29 female and nine male patients. For radiographic evaluation we used the standing antero-posterior and lateral projections of the thoracic and lumbar spine, preoperatively and at least one year postoperative. We assessed the frontal and sagittal Cobb angles. The angles were all measured by the same investigator (second author).

Results: Using Pearson correlation analyses we found a significant correlation (p< 0.001) between the relative (%) corrections of thoracic and lumbar curves (table1). The correlation coefficient between the relative correction of the thoracic and lumbar curve decreased with the Lumbar modifier (A, B, C).

Conclusion: A significant correlation is present between the relative corrections of the main thoracic curve and the lumbar curve after selective thoracic fusion in idiopathic scoliosis. The recently introduced new classification system seems to be of great predictable value for the spontaneous correction of the lumbar curve. Depending on the curve-type, a different technique for predicting the outcome should be used.