He Z, Qin X, Yin R, et al. - Researchers tried to find out if the rotation of preoperative-presumed lowest instrumented vertebra (LIV) is a risk factor for adding-on (AO) in adolescent idiopathic scoliosis (AIS) treated with selective posterior thoracic fusion (sPTF). This study recruited a sum of 196 AIS individuals of Lenke type 1A or 2A with a minimum 2-year follow-up after sPTF with all pedicle screw instrumentation. They assessed radiographical parameters as follows: preoperative rotation angle of presumed LIV and LIV + 1, LIV + 1/LIV rotation difference, postoperative rotation angle of LIV and LIV derotation angle on CT scans. Individuals were divided into the AO group and the non-AO group during the follow-up. Between the two groups, the parameters were correlated to examine risk factors for AO. Adolescent idiopathic scoliosis individuals with low Risser grade and large preoperative rotation angle of presumed LIV are more likely to occur with AO after sPTF. Furthermore, preoperative rotation of presumed LIV might be still a risk factor correlated with the occurrence of AO for the individuals with LSTV selected as LIV.