ABSTRACT
<p><b>OBJECTIVE</b>To establish criteria for AIS of Lenke5 and Lenke6 by an anterior only procedure of the lower curve fusion.</p><p><b>METHODS</b>A retrospective study was conducted between March 1999 and May 2004 to investigate 52 AIS patients of Lenke5 and Lenke6. All the patients were observed 24 years (34 months on average). Many parameters were evaluated. At final assessment, two groups emerged: Group A had satisfactory results (the thoracic curve was reduced) and Group B had just the opposite.</p><p><b>RESULTS</b>Preoperative thoracic curve in group A averaged 33 degrees and 18 degrees after surgery. The lumbar curve averaged 49 degrees before surgery and 21 degrees after surgery. In group B (n = 6), the average thoracic curve was 38 degrees before surgery and 45 degrees after surgery, whereas the lumbar curve averaged 46 degrees before surgery and 25 degrees after surgery. Two of these patients underwent posterior thoracic instrumentation and fusion because of the unreasonable balance.</p><p><b>CONCLUSIONS</b>A successful surgical outcome was dependent on both the flexibility of the thoracic curve and the patients' maturity. The thoracolumbar/lumbar-thoracic (TL/L:T) Cobb ratio in combination with the flexibility of the thoracic curve were the best predictors among the structural indexes.</p>