Abstract:Adolescent Idiopathic Scoliosis (AIS) is the most common scoliosis deformity. Distal adding-on is a common complication after selective posterior thoracic fusion in AIS patients. adding-on phenomenon can affect the quality of life of patients. The main risk factors reported in the previous literature include the selection of lowest instrumented vertebra, growth potential, factors related to thoracic curvature and lumbar curvature, L4 vertebral tilt direction, shoulder balance, coronal balance, etc. However, there is still controversy about the risk factors of adding-on phenomenon. This article reviews the definition, epidemiology, risk factors and prevention of adding-on phenomenon in order to further understand this complication.