Selection of the lower instrumented vertebra in adolescents with thoracic scoliosis secondary to Chiari malformation

Objective To investigate the effect of lowest instrumented vertebrae (LIV) selection on clinical outcome of posterior thoracic fusion in adolescents with thoracic scoliosis secondary to Chiari malformation.Methods total of 27 adolescents with Chiari malformation-associated scoliosis,who had undergone posterior thoracic fusion and been followed up for at least 2 years,were enrolled in this study.There were 11 males and 16 females,with an average age of 15.2 years (range,12 to 18 years).The following radiographic parameters:coronal Cobb angle,curve flexibility,apical vertebral translation (AVT),apical vertebral rotation (AVR),trunk shift (C7PL-CSVL distance),thoracic kyphosis (TK),lumbar lordosis (LL),thoracolumbar kyphosis,and sagittal vertical axis (SVA) were recorded preoperatively,immediately after surgery and at the last follow-up.Results All the patients received a followed-up from 2 to 7 years (average,3.4years).At the last follow-up,the average correction rate of thoracic curve was 55.9％ with an average correction loss rate of 2.3％.The spontaneous correction rate of lumbar curve was 59.2％ on average.At the last follow-up,no significant difference in terms of the radiographic parameters was found between patients with lumbar modifier A and B.In patients having the lumbar modifier A,the LIV was at L1 in 6 cases and at L2 in 7 cases.As for those with lumbar modifier B,the LIV located at L1 in 6 cases,L2 in 4 cases,and T12 in 1 case.Among patients with lumbar modifier B,the LL was significantly higher in cases with LIV at L1 when compared with those with LIV at L2.Conclusion Selective thoracic fusion can provide a satisfactory outcome in adolescents with Chiari malformation-associated scoliosis with lumbar modifier A and B. Key words: Armold-Chiari malformation;  Scoliosis;  Thoracic vertebrae;  Spinal fusion