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 lumbosacral 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-grade, 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 the no-LSTV group and on L5 in the high-grades were compared. Results. Seven hundred thirteen subjects were included, of whom 23 low-grades and 27 high-grades. The mean pelvic incidence was 51.0±11.0°, and the 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. Conclusions. 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.