BACKGROUND CONTEXT LIV Selection in AdIS patients fused short of the sacrum is still debatable. Multiple radiographic methods have been devised to determine LIV, however, there is no universal standard. The TV rule for LIV determination has previously been described as providing acceptable LIV positioning on long-term follow-up in Adolescent Idiopathic Scoliosis (AIS) Lenke type-1 and -2 curves. We investigated whether the TV could be employed for guiding LIV selection in AdIS patients fused short of sacrum (LIV = L4 and above). PURPOSE The TV has been demonstrated as a reliable way to select the LIV in AIS. Here we sought to determine whether the TV rule is a reliable method for LIV selection in AdIS patients fused short of the sacrum. STUDY DESIGN/SETTING Single center/surgeon retrospective study. PATIENT SAMPLE Radiographic review of 52 patients with AdIS treated between July 2015 and December 2019. OUTCOME MEASURES CSVL-LIV distance determined on standing AP radiographs. METHODS AdIS patients treated by senior author between 2015 and 2019, with LIV L4 or above, and a minimum of 1-year radiographic follow-up (range: 1- 3 years) were included. The TV was determined on preoperative standing AP radiographs as the most cephalad lumbar vertebra “touched” by the center sacral vertical line (CSVL) and then compared to the LIV. Postoperative LIV position was evaluated in relation to the CSVL and the offset (CSVL-LIV distance) compared among patients fused cephalad-, caudad- and to the TV. RESULTS Fifty-two AdIS patients with ≥ 1 year of follow-up were available for review. Of these, 18 (35%) had fusion to the TV, 21 (40%) cephalad to the TV, and 13 (25%) caudad to the TV. Patients fused cephalad of the TV (TV≤-1) had larger CSVL-LIV distance (1.71±0.54 cm) on follow-up compared to those who had fusion to the TV (0.92±0.58cm) [p=0.05]. Patients who had fusion caudad to the TV (TV≥+1) had a shorter CSVL-LIV distance (0.7±0.58cm) compared to those fused to the TV, but this was not statistically significant. CONCLUSIONS Fusion to, or caudad to, the TV in AdIS results in significantly lower CSVL-LIV translation on radiographic follow-up compared to fusion cephalad to the TV. However, fusion caudad to the TV incurs fewer distal mobile segments, but with no significant benefit in decreasing CSVL-LIV translation, and thus fusion to the TV appears to be the best option in AdIS patients fused short of the sacrum. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. LIV Selection in AdIS patients fused short of the sacrum is still debatable. Multiple radiographic methods have been devised to determine LIV, however, there is no universal standard. The TV rule for LIV determination has previously been described as providing acceptable LIV positioning on long-term follow-up in Adolescent Idiopathic Scoliosis (AIS) Lenke type-1 and -2 curves. We investigated whether the TV could be employed for guiding LIV selection in AdIS patients fused short of sacrum (LIV = L4 and above). The TV has been demonstrated as a reliable way to select the LIV in AIS. Here we sought to determine whether the TV rule is a reliable method for LIV selection in AdIS patients fused short of the sacrum. Single center/surgeon retrospective study. Radiographic review of 52 patients with AdIS treated between July 2015 and December 2019. CSVL-LIV distance determined on standing AP radiographs. AdIS patients treated by senior author between 2015 and 2019, with LIV L4 or above, and a minimum of 1-year radiographic follow-up (range: 1- 3 years) were included. The TV was determined on preoperative standing AP radiographs as the most cephalad lumbar vertebra “touched” by the center sacral vertical line (CSVL) and then compared to the LIV. Postoperative LIV position was evaluated in relation to the CSVL and the offset (CSVL-LIV distance) compared among patients fused cephalad-, caudad- and to the TV. Fifty-two AdIS patients with ≥ 1 year of follow-up were available for review. Of these, 18 (35%) had fusion to the TV, 21 (40%) cephalad to the TV, and 13 (25%) caudad to the TV. Patients fused cephalad of the TV (TV≤-1) had larger CSVL-LIV distance (1.71±0.54 cm) on follow-up compared to those who had fusion to the TV (0.92±0.58cm) [p=0.05]. Patients who had fusion caudad to the TV (TV≥+1) had a shorter CSVL-LIV distance (0.7±0.58cm) compared to those fused to the TV, but this was not statistically significant. Fusion to, or caudad to, the TV in AdIS results in significantly lower CSVL-LIV translation on radiographic follow-up compared to fusion cephalad to the TV. However, fusion caudad to the TV incurs fewer distal mobile segments, but with no significant benefit in decreasing CSVL-LIV translation, and thus fusion to the TV appears to be the best option in AdIS patients fused short of the sacrum.