Abstract
Background: This study aimed to evaluate the relationship between thoracolumbar kyphosis (TLK) and lumbar degenerative spondylolisthesis (LDS) and to determine whether TLK can serve as an independent radiological predictor for both the presence and the specific affected level of LDS. Methods: Initially, 211 patients were screened for this study. After applying exclusion criteria, a final cohort of 129 patients (76 women and 53 men; mean age 62.1 ± 9.1 years) who underwent surgical intervention for degenerative lumbar spinal stenosis and had preoperative full-spine standing radiographs were retrospectively analyzed. Patients were divided into two groups: an LDS group (n = 54) comprising patients with concurrent degenerative spondylolisthesis, and a control group (n = 75) consisting of surgical patients without spondylolisthesis. Sagittal parameters, including TLK (T10-L2 angle), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), and thoracic kyphosis (TK), were measured. LDS was classified by the affected level (L3-L4, L4-L5, L5-S1). Group differences were compared, ROC analysis was performed to identify a threshold value, and multivariate logistic regression was used to determine independent predictors. Results: Multivariate analysis revealed that the T10-L2 angle (TLK) (OR: 1.15, p = 0.001), sacral slope (OR: 1.40, p = 0.017), pelvic tilt (OR: 1.50, p = 0.003), pelvic incidence (OR: 0.68, p = 0.004), and lumbar lordosis (OR: 1.09, p = 0.005) were significant independent predictors of LDS. Conversely, global thoracic kyphosis (TK) demonstrated an inverse relationship (OR: 0.88, p = 0.001), indicative of a secondary compensatory adaptation. ROC analysis established a TLK cut-off of ≥19.5° (AUC = 0.68, p = 0.001) for predicting LDS. Furthermore, Roussouly Type 3 alignment was significantly more prevalent in the L5-S1 LDS cohort (48.1%) Conclusions: Increased TLK is independently associated with LDS, particularly at lower lumbar levels. A TLK value ≥ 19.5° may serve as a practical radiographic marker, and TLK assessment should be incorporated into sagittal alignment evaluation and surgical planning.