Summary of Background Data.Thoracolumbar/Lumbar scoliosis is a common type of adolescent idiopathic scoliosis which is classified to Lenke type 5.Anterior spinal fusion (ASF) with single or dual rod has been used for many years and has become a common method of correction for these type of curve since 20 years ago.Compared to posterior correction and spinal fusion (PSF), ASF has its great advantages of short fusion, mobility of lumbar spine reservation.But in clinical observation, we found some patients appeared trunk imbalance at early stage or in long term postoperatively due to short fusion which beyond the compensative ability of unfused levels.In our understanding, few study has investigated the relationship between saving fusion levels and trunk balance about anterior correction.This study analyzed radiographic parameters of 28 thoracolumbar/lumbar adolescent idiopathic scoliosis patients who had complete follow-up datas.The surgical strategy of selection of lower instrumented vertebra (LIV) was evaluated to find the criteria of determination for LIV preoperatively.Objective.To investigate surgical strategy of lowest instrumented vertebrae (LIV) selection of anterior correction for adolescent idiopathic scoliosis, and to discuss correlation of lowest instrumented vertebrae and trunk balance.Methods.From 1998 to 2004, Twenty-eight patients with thoracolumbar/lumbar adolescent idiopathic scoliosis (Lenke 5 type) were treated by anterior correction and fusion with mean 1.5-year follow-up.Specific radiographic parameters such as LIV and fusion levels, disc wedging, LIV obliquity, global coronal balance were observed respectively, and correlation of disc wedging and these parameters was analyzed.This study evaluated the LIV selection by three statistics analysis as followed.The disc angle (DA) and absolute disc angle at two weeks postoperative and up to 5 years of follow-up were analyzed with regard to their influence by the LIV relative to the LEV with analyses of variance (ANOVA).Mixed-model repeated measures ANOVA was used if these datas changed over time.Univariate repeated analysis was used to compared LEV-LIV correlation (+1,0,-1) and various preoperative radiographic parameters.LIV selection was assessed through postoperative parameters.Coronal balance were demonstrated by 3 parameters at last follow-up: disc angle; LIV translation; global balance (T1-CSVL).The correlation of each radiographic parameters and these three were analyzed respectively by use of Pearson correlation and stepwise multiple linear regression.The stepwise regression selected independent variables for inclusion or exclusion from the model base on entry criteria of 0.15 and removal criteria of 0.15.All statistical analyses were treated by the Statistical Analysis System.Results.Mean corrective rate of major curve was 74.84%.The preoperative disc angle was 2.96o±1.43o and postoperative was-3.60 o-±1.75 o.The postoperative disc wedging was most correlated with LIV obliquity.Trunk balance and LIV-CSVL distance, fusion segments, LIV obliquity were significant correlated.The correlation ofposteroperative LIV-CSVL distance which reflects regional balance with various preoperative parameters, in which fusion levels, T12-L2 lordosis, segments of Apex-LIV, preoperative DA, LIV obliquity and T1-CSVL distance were correlated.Conclusion.Selection of LIV was correlated with various radiographic parameters.Short fusion was inappropriate in such conditions: big disc angle of lower end vertebrae between superior vertebrae , fewer vertebra between certain vertebrae and apex vertebrae, long distance from certain vertebrae to CSVL and lager obliquity of the vertebrae.Disc wedging distal to LIV tent to occur postoperatively if parallel disc was not involved.