The Implications of Sacralized Transitional Vertebra on Spinal Alignment

Study design: Retrospective study of a multicentric prospective database. Objective: This study aimed to determine, in a cohort of healthy volunteers, the impact of sacralized lumbo-sacral transitional vertebra (LSTV) on spinal alignment according to its grade, particularly regarding lumbar lordosis magnitude and distribution, and the implications for spinopelvic parameters measurement. Summary of Background Data: There is little data regarding spinopelvic alignment assessment in LSTV patients. Methods: This study included healthy volunteers with full-body stereoradiographs in free-standing position aged over 18. Castellvi grade, pelvic parameters (measured on S1 and L5), L1-S1 lumbar lordosis (LL) and segmental lordosis for each disc and vertebral body, thoracic kyphosis, cervical lordosis, lower limb, and global alignment parameters were assessed. Castellvi I and II were considered as Low-grade and Castellvi III and IV as High-grade LSTV. Alignment parameters between No-LSTV, Low- and High-grade LSTV were compared. Propensity score matching was used to match PI in No-LSTV and Low-grades. Spinopelvic parameters measured on S1 in No-LSTV group and on L5 in High-grade were compared. Results: 713 subjects were included, of whom 23 Low-grades and 27 High-grades. Mean pelvic incidence was 51.0±11.0° and mean age was 37.5±16.2 years. LL distribution was different between groups, with an apex and inflexion point significantly higher in High-grade ( P<0.001 ). Kyphosis in the LSTV segment was compensated for by a steeper increase of LL above L5 in the High-grades. Low-grades and PI-matched No-LSTV presented similar alignment parameters. There were minor differences in parameters measured on S1 in No-LSTV and no L5 in High-grades. Conclusion: Subjects with low-grade LSTV present similar alignment as PI-matched No-LSTV subjects, and S1 should be taken as reference to measure spinopelvic parameters. High-grade LSTV subjects have kyphotic L5-S1 segment with more cranial lumbar apex and thoracolumbar inflexion point. In these subjects, spinopelvic parameters should be measured on L5.