Impact of incidental thoracic spinal stenosis on outcomes following lumbar fusion: propensity score-matched cohort study.

BACKGROUND: Incidental thoracic spinal stenosis (TSS) is increasingly identified on whole-spine imaging, but its clinical significance in patients undergoing lumbar fusion remains unclear. This study aimed to evaluate whether incidental radiologic TSS is associated with postoperative outcomes following lumbar fusion. METHODS: A retrospective propensity score-matched cohort study was conducted using a prospectively maintained registry [2010-2023] at a single tertiary centre. Patients with incidental radiologic TSS were matched 1:4 to controls without TSS based on age, sex, body mass index, and number of fused levels. Outcomes included Visual Analogue Scale (VAS), Oswestry Disability Index (ODI), North American Spine Society (NASS), and 36-Item Short Form Health Survey (SF-36) at baseline, 6 months, and 2 years. RESULTS: Both groups demonstrated meaningful improvements in pain, disability, and quality-of-life outcomes at 6 months and 2 years. No significant between-group differences were observed in pain, disability, or quality-of-life outcomes at 6 months or 2 years (all P>0.05). During follow-up, 9/27 patients (33.3%) with TSS required thoracic surgery, whereas none in the control group did. CONCLUSIONS: In this propensity score-matched cohort, no statistically significant differences in lumbar fusion outcomes were detected between patients with and without incidental radiologic TSS at 6 months or 2 years. However, the subsequent thoracic surgery rate of 33.3% suggests that incidental TSS should not be considered clinically benign and may warrant ongoing surveillance for neurological progression.