Purpose of the study To analyze post operative imbalance after C.D.I (Cotrel Dubousset Instrumentation) for idiopathic scoliosis according to the fused area, particularly the lower level of fusion. To recall a classification for: determination of fusion area based on preoperative standing coronal radiograph. Patients and methods To be included in this study the patients had to have an adolescent idiopathic scoliosis, at least two years of post operative follow up. 122 patients met the criteria; mean follow up was 3 years, 5 months (minimum 2 years; maximum 9 years). Scoliotic curves were classified as single structural (81), double structural (41); Balance was clinically analyzed bu plumbline, radiographically by a plumbline dropped from C7 to the sacrum and measuring deviation from the midpoint of the sacrum in centimeters. A curve with a deviation of 10 mms or less was considered as balanced. Results Imbalance in angle structural curves was 70% when using stable vertebra (King) or "other vertebra" (beyond stable vertebra or one or two levels upper stable yertebra). Using end vertebra (J. Moe), (elected vertebra, C. Salanova) imbalance was 10%. In double structural (41 cas) imbalance was 50% using stable, or "other vertebra" 10% when elected vertebra was fused. Discussion In this study there was a strong relationship between the lower level of fusion and imbalance.
