Relationship of T10-Pelvic Angle With Conventional Sagittal Parameters and Legacy Alignment Schemes in Adult Spinal Deformity Surgery

Study Design: Retrospective analysis. Objective: To investigate the relationship of T10-pelvic angle (T10PA) with conventional sagittal parameters and legacy alignment schemes. Summary of Background Data: T10PA is a newly introduced sagittal parameter to predict the development of proximal junctional kyphosis (PJK). However, its relationship with conventional sagittal parameters and legacy alignment schemes remains unknown. Methods: Patients with fusion from the pelvis to the upper-instrumented vertebra at or above the T10 were included. Based on the 6-week T10PA, the patients were divided into 3 groups as follows: undercorrection, functional alignment, and overcorrection. Conventional sagittal parameters and alignment status based on the Schwab’s pelvic incidence (PI)–lumbar lordosis (LL) modifiers and age-adjusted PI–LL were compared according to the T10PA groups. The PJK rates were compared among the alignment schemes. Results: Overall, 219 patients were enrolled in this study. At 6 weeks postoperatively, 33.3%, 37.0%, and 29.7% of the patients demonstrated undercorrection, functional alignment, and overcorrection relative to the T10PA, respectively. Conventional sagittal parameters significantly differed according to the T10PA groups. Linear regression analysis revealed that T10PA was significantly affected by PI (β = .562) and LL (β = − .411). The correction statuses of the Schwab’s PI–LL modifiers and age-adjusted PI–LL were significantly differentiated between the T10PA correction groups. However, only 32.9% of patients with functional alignment relative to T10PA belonged to matched correction category for the age-adjusted PI–LL. Overcorrection relative to age-adjusted PI–LL and T10PA significantly increased PJK risks. Conclusion: T10PA significantly correlated with conventional sagittal parameters, particularly PI and LL. Although the T10PA correction status correlated with that of the legacy alignment schemes, a notable discrepancy in the optimal correction was observed between the T10PA and age-adjusted PI–LL schemes. Overcorrection relative to T10PA and age-adjusted PI–LL should be avoided to mitigate PJK development.