Association between thoracic kyphosis and objectively measured sleep efficiency in patients with lumbar spinal stenosis

Purpose Sleep disorders frequently occur in patients with lumbar spinal stenosis (LSS), but the role of sagittal spinal alignment in these disorders remains unclear. This study aimed to examine the association between sagittal alignment parameters and objectively measured sleep quality in LSS patients, with a particular focus on thoracic kyphosis (TK). Methods Patients with LSS were prospectively enrolled in a single-center cross-sectional study. Sleep parameters, including sleep efficiency (SEf), wake after sleep onset (WASO), and mean active count (MAC), were assessed using a wrist-worn accelerometer. Spinopelvic alignment was evaluated using standing radiographs and supine CT scans. Associations between sleep parameters and clinical variables were assessed using Spearman's rank correlation and multivariate regression analysis with SEf as the dependent variable. Results Seventy patients were analyzed. Greater TK was significantly associated with higher MAC, longer WASO, and lower SEf. In multivariate analysis, TK (β = -0.250, p = 0.027), ODI (β = -0.286, p = 0.003), and pregabalin/mirogabalin use (β = -0.368, p = 0.006) were independently associated with SEf (adjusted R² = 0.266). Other malalignment parameters and lower-limb pain were associated with reduced nocturnal movements but not significantly with SEf. Conclusion Excessive TK was identified as an independent determinant of reduced SEf in LSS patients. These findings suggest that abnormal sagittal alignment, particularly thoracic curvature, adversely affects nighttime recovery beyond pain and functional impairment, emphasizing the importance of considering spinal alignment in the management of LSS-related sleep disorders.