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

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. RESULTS: One 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. These slides can be retrieved under Electronic Supplementary Material.

Thoracolumbar Junction Orientation: A Novel Guide for Sagittal Correction and Proximal Junctional Kyphosis Prediction in Adult Spinal Deformity Patients.

BACKGROUND: Novel radiographic sagittal parameters of the thoracolumbar junction orientation (TLJO, thoracolumbar slope [TLS] and thoracolumbar tilt [TLT]) have been introduced and correlated with lumbopelvic parameters and thoracic kyphosis. OBJECTIVE: To determine a predictive model for reciprocal thoracic kyphosis and proximal junctional kyphosis (PJK) based on the TLJO. METHODS: A total of 127 patients who had fusion from sacrum to T10-L2 from 2004 to 2014 were reviewed. TK (T5-T12), PI, SS, PT, LL, and proximal junctional angle (PJA) were measured preoperatively, 6 wk postoperatively, and at final follow-up. TLJO was measured by TLS and TLT. Changes between time points were determined (preop-6 wk = ΔParameterPre6wk and preop-final follow/up = ΔParameterPreFinal). Scoliosis Research Society (SRS) and Oswestry Disability Index (ODI) questionnaires were evaluated at final follow-up. Patients were divided into 2 groups based on the presence of PJK (ΔPJAPreFinal >15°). Independent t-tests and receiver operating characteristic (ROC) curves were used to investigate the significance of differences and cut-off values. Pearson correlations and linear regressions were used to analyze the entire cohort to determine the relationship between the changes in parameters. RESULTS: Compared to patients without PJK (n = 100), those with PJK (n = 27) had significantly lower SRS scores and significantly greater ΔTKPreFinal, ΔLLPre6wk, and ΔTLSPre6wk. To maintain in the nonPJK group, ROC curves demonstrated a cut-off value of -9.4° for ΔTLSPre6wk. PJK was significantly correlated with ΔTKPreFinal and ΔTLSPre6wk. The linear correlation revealed that ΔTLSPre6wk < -25.3° is the risk factor of PJK > 15°. CONCLUSION: As change of TLS reflects lumbopelvic realignment and influences reciprocal TK, reducing the change of TLS may be a sagittal realignment guideline to reduce the risk of PJK.