Increased Preoperative Segmental Lordosis Is Associated With Elevated Rates of Pseudoarthrosis After L5–S1 Transforaminal Lumbar Interbody Fusion

Study Design: Retrospective cohort study. Objective: To evaluate the predisposing factors to pseudoarthrosis in patients undergoing one-level L5–S1 TLIF. Background: Transforaminal lumbar interbody fusion (TLIF) at the lumbosacral junction is frequently performed for degenerative pathology, yet pseudarthrosis remains a clinically significant complication. The role of preoperative segmental alignment in predicting pseudoarthrosis at L5–S1 has not been well established. Materials and Methods: We conducted a retrospective cohort study of 151 patients undergoing single-level L5–S1 TLIF between 2018 and 2022 at a single academic center, with ≥2 years of follow-up. Patients were stratified by the presence of pseudarthrosis, defined radiographically. Demographics, preoperative sagittal parameters, and complications were analyzed. Multivariate regression identified independent predictors, and Kaplan–Meier and Cox proportional hazards modeling evaluated reoperation risk. Results: Pseudarthrosis occurred in 13 patients (8.6%). While age, sex, BMI, smoking status, and comorbidity index were not associated with pseudoarthrosis, patients with pseudarthrosis had significantly greater preoperative L5–S1 segmental lordosis (24.4° vs . 17.3°, P < 0.001) and reduced L4–L5 anterior disc height (9.0 vs . 12.2 mm, P = 0.015). Both remained independent predictors on adjusted analysis (lordosis OR: 1.28, P = 0.001; disc height OR: 0.78, P = 0.012). Pseudarthrosis was associated with increased reoperation (53.8% vs . 15.9%, P = 0.002). Survival analysis demonstrated a >4-fold increased hazard of reoperation (HR: 4.49; 95% CI: 1.87–10.76; P < 0.001). Conclusions: Pseudarthrosis following single-level L5–S1 TLIF was associated with hyperlordotic preoperative alignment and reduced adjacent-level disc height, and carried substantially higher risks of overall and earlier reoperation. Careful evaluation of segmental morphology and adjacent-level degeneration may aid in identifying patients at greatest risk and optimizing surgical planning. Level of Evidence: Level IV.