Objective:To introduce a key-vertebral-screws technique(KVST) in the surgical treatment of scoliosis extending to main thoracic levels,and to find the role of fulcrum bending in predicting the result of surgical treatment for scoliosis by this technique.Methods:Seventeen consecutive patients with scoliosis extending to main thoracic spine,who underwent pure posterior fusion without anterior or posterior release by KVST between January 2004 and July 2005 were evaluated for fulcrum bending flexibility,surgical correction rate,fulcrum bending correction index (FBCI) in main thoracic curves.Universal Spine System (USS) instrumentation was used in 15 cases,Monarch in another 2 cases.The severity of the curves was measured by Cobbs method using RadWork 6.0 software.Preoperative standing AP radiographs,preoperative fulcrum bending anterioposterior (AP) radiographs,postoperative standing AP radiographs,and most recent follow-up standing AP radiographs for spine were measured and recorded.All the data were analyzed with two-sample paired t-test by Origin 7.0 software.Results:Infection and neurological complications were not noted.No major complications were found.Just one case had some axial back pain,which got a full recovery from physiotherapy for 2 weeks.In the X-ray,there was an average correction of 71.5% of the fused main thoracic curves,which had no significant lose of correction in final follow-up.For the whole fused main thoracic curves,the fulcrum bending flexibility were lower to operation correction rate (P=0.013).The average FBCI was 123%.From the data,the more rigid curves (especially fulcrum bending flexibility＜50%),the more correction rate operation could get,compared with fulcrum bending flexibility.Conclusion:(1) KVST is a good method in the surgical treatment of thoracic scoliosis,which can get satisfying result with lower medical cost.(2) Fulcrum bending flexibility is lower than operative correction rate by KVST in main thoracic curves (P＜0.05).In the more rigid curves assessed by fulcrum-bending radiograph,the operative corrective could be gained,especially in the curves which FBCI is lower than 50%.