AIM: To evaluate the orientation of the sacrum, its influence on sagittal balance, and its practical relevance in identifying a sacralized L5 or lumbarized S1 as a lumbosacral transitional vertebrae (LSTV) to help prevent complications. MATERIAL and METHODS: Lumbosacral vertebral roentgenograms from 633 outpatients who visited our hospital between June 2018 and August 2018 were retrospectively reviewed. RESULTS: All participants were young males with a mean age of 18.41 years (range 17-21 years). The mean ATA1 distance was 16.84 mm ± 6.28 in the 527 normal cases, 4.21 mm ± 5.32 in the 71 sacralization cases, and 21.17 mm ± 6.68 in the 35 lumbarization cases. The angle distribution among the 527 patients with normal anatomy was 10.58° ± 1.3. In the 71 patients with sacralization, the angle was 8.89° ± 1.13. Among the 35 patients with lumbarization, the angle was 9.86° ± 1.76. CONCLUSION: A new index formula, comprising the Anterior Translational Arch (ATA1) and Anterior Translational Angle (ATA2) is proposed. ATA1 as a distance measurement and ATA2 as an angular measurement were evaluated. These measurements can be easily obtained using either lumbosacral vertebral radiographs or sagittal MRI, owing to the simplicity of the calculation. This allows an easy identification of lumbarization and sacralization.