Thoracolumbar junction orientation: its impact on thoracic kyphosis and sagittal alignment in both asymptomatic volunteers and symptomatic patients

Abstract

Purpose The thoracolumbar junction (TLJ) has not been explored in regard to its contribution to global sagittal alignment. This study aims to define novel sagittal parameters of the TLJ and to assess their roles within global sagittal alignment. Methods Included for cross-sectional, retrospective analysis were asymptomatic volunteers and symptomatic patients who had undergone operation for adult spinal deformity. Unique sagittal parameters of the TLJ were measured using the midline of the T12-L1 disk space: The TLJ orientation [TLJO; thoracolumbar tilt (TLT) and slope (TLS)]. Thoracic kyphosis (TK; T5-12), C7-S1 sagittal vertical axis (SVA), lumbar lordosis (LL; L1-S1), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI) were measured. Continuous variables were compared using the independent t test. Pearson correlations examined relationships between the parameters in each group. The asymptomatic TK was calculated using the measurement of the asymptomatic volunteer's TLJO by linear regression. ResultsOne hundred fifteen asymptomatic volunteers and 127 symptomatic patients were included. Only LL among the lumbopelvic parameters correlated with TK (asymptomatic volunteers: r = − 0.42; symptomatic patients: r = − 0.40). All the pelvic parameters have no direct correlation with TK in both groups. TLJO had stronger correlation with TK [asymptomatic volunteers: r = − 0.68 (TLS), r = 0.41 (TLT); symptomatic patients: r = − 0.56 (TLS), r = 0.44 (TLT)] than the lumbopelvic parameters. TLS correlated with LL (asymptomatic volunteers: r = 0.78; symptomatic patients: r = 0.73). Most pelvic parameters correlated with TLJO except for PI. The asymptomatic TK was estimated by the derived formula: 20.847 + TLS × (− 1.198). Conclusion The TLJO integrates the status of the lumbopelvic sagittal parameters and simultaneously correlates with thoracic and global sagittal alignment.

Thoracolumbar Slope Is Useful Parameter for Evaluating HealthRelated Quality of Life and Sagittal Imbalance Aggravation in Adult Spinal Deformity: A Prospective Observational Cohort Study

“…Among them, TLS most highly correlated with ODI score (r = 0.374, p = 0.002). Multivariate logistic regression analysis showed that TLS greater than -3.5°, which is the mean value in patients with PDSI who require surgical treatment due to clinical symptoms, 11 was a predicting factor for PDSI aggravation (p = 0.034; confidence in- terval, 1.173-63.61; odds ratio, 8.636). A BMI greater than 25 kg/m 2 , which is the criterion for overweight; an SVA greater than 9.5 cm, which is the criterion for marked deformity 8 ; and a T1PA greater than 30° were not significant predictors for PDSI aggravation (Table 5).…”

“…PDSI is understood as the cumulative result of degenerative changes and the natural progression of aging. 11,17 In a longitudinal study of age-related changes in sagittal spinal alignment in 237 individuals over a 4-year period, Oe et al 18 reported that SAPs deteriorated with age, including SS, PT, LL, T1 slope, cervical lordosis, and SVA in the seventh-decade female group. Many elderly individuals experience mild sagittal imbalance, but PDSI does not deteriorate in all individuals with aging.…”

“…3 Moreover, SAPs that are measured using Cobb angle through 2 or more endplates are more likely to have erroneous measurements. 21 Recently, Moon et al 10,11 re-ported novel SAPs of the thoracolumbar junction, including TSL and TLT, categorizing them as thoracolumbar junction orientation (TLJO). To measure TLS, whole-spine lateral radiography is not required, and because only the L1 endplate needs to be clearly identified, measurement errors are reduced and the reliability is high (Fig.…”

“…Before enrolling subjects, we checked the whole-spine standing radiographs to confirm that the volunteers had SVA larger than 50 mm. 11…”

“…1). 9,11 Based on serial analysis, PDSI aggravation was defined as a T1PA increase of more than 3° and SVA increase of more than 30 mm compared to baseline value. 1 The back and lumbar muscle volumes were measured based on the cross-sectional areas of the lumbar multifidus muscle (MF), lumbar erector spinae muscle (ES), and psoas muscle (PS).…”