Background Data: In adolescent idiopathic scoliosis (AIS), the upper thoracic spine (T1–T5) may represent an additional curve called the proximal thoracic curve (PTC), which is nearly equal and opposite to the main thoracic curve (MTC); this is a classic example of a ‘‘double thoracic curve pattern." So, after selective thoracic fusion (STF) for MTC by either anterior or posterior instrumentation and fusion, what happens to the noninstrumented PTC and instrumented MTC? Study Design: Systematic review of literature and meta-analysis. Purpose: To evaluate the fate of the noninstrumented PTC and instrumented MTC after STF for the MTC by either anterior or posterior instrumentation and fusion. Methods: This study was conducted by searching the PubMed and Cochrane databases and included patients with AIS treated by STF between 1999 and 2020. The type of approach, degree of correction achieved in MTC, PTC, and apical vertebral rotation (AVR), and complications rate were reported independently by two authors. Results: Our systematic review yielded 1686 patients, with 18 studies meeting the required criteria. MTC has been corrected by 24.89 ± 8.45 degrees, while PTC has been corrected by 14.94 ± 7.18 degrees. Cobb's angle was reported in seven studies for MTC angle and four studies for lumbar and thoracolumbar curves angle and has been corrected by 19.68 ± 6.55 degrees. Moreover, shoulder tilt has been corrected by 0.83 ± 0.83. Data for correction of AVR was reported in two studies and has been corrected by 15.95 ± 4.65 degrees. Conclusion: Anterior and posterior spinal fusion had no statistical significance difference regarding MTC, shoulder tilt, and AVRcorrection. However, PTC corrections was more significant after anterior spinal fusion (ASF) than posterior spinal fusion (PSF). (2021ESJ228)