Spinopelvic alignment and sagittal balance of asymptomatic adults with 6 lumbar vertebrae

The purpose of this study was to evaluate total spinal alignment in asymptomatic individuals with 6 lumbar vertebrae (LVs).

The present study comprised 167 Japanese adult volunteers with no spinal symptoms. In all individuals, standing radiographs of the entire spine were taken to measure the pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), C7 sagittal vertical axis (C7SVA), T1 slope, thoracic kyphosis (TK), C2-C7 sagittal vertical axis (C2-C7 SVA), and C2-C7 lordosis (C2-C7L). We used these parameters to compare individuals with 5LVs to those with 6LVs. We performed additional investigations regarding the relationship between L6 morphological characteristics and parameters.

Out of 167 individuals, 6LVs were present in 29 (17.4 %). PI was significantly greater in individuals with 6LVs (64.8° ± 9.54°) than in those with 5LVs (51.3° ± 10.1°, P < 0.0001). Individuals with 6LVs also had significantly larger SS, PT, and C7SVA values (SS: P = 0.0125, PT: P < 0.0001, C7SVA: P = 0.0172). LL tended to be nonsignificantly greater in individuals with 6LVs (P = 0.1588). All of these changes were more noticeable in individuals in whom the L6 vertebra was classified as type II and III according to the Castellvi classification. Meanwhile, the presence of 6LVs has little influence on the alignment of the superior lumber vertebrae.

Asymptomatic individuals with 6LVs presented with different spinopelvic alignment compared to those with 5LVs. We need to establish a treatment strategy for symptomatic 6LV cases.