L5-S1 Transforaminal Lumbar Interbody Fusion (TLIF) Is Associated with Increased Revisions Compared to L4-L5 TLIF at Two Years

Study Design. Retrospective cohort study. Objective. Compare outcomes in patients undergoing one-level transforaminal lumbar interbody fusion (TLIF) at L4-S1. Background. TLIF is frequently performed at L4-S1 to treat degenerative lumbar pathologies. However, the native alignment and biomechanics differ across L4-L5 and L5-S1, and there is limited data regarding comparative radiographic outcomes. Methods. Patients who underwent one-level TLIF at L4-L5 or L5-S1 at a single academic institution were identified. Baseline demographics, procedural characteristics, change in postoperative spinopelvic alignment and patient-reported outcome measures (PROMs), and two-year postoperative surgical complications were compared. Multivariate regression analyses, accounting for age, gender, Charlson Comorbidity Index (CCI), and body mass index (BMI), were also performed. Results. Across the 175 included patients, 125 had L4-L5 TLIF and 50 had L5-S1 TLIF. The mean age was 57.8 years, 56.6% were female, mean CCI was 0.9, and mean follow-up was 26.7 months. In the hospital, the two cohorts were not statistically different with regards to EBL and LOS. Two years postoperatively, multivariate linear regression analyses revealed that L5-S1 TLIF achieved 6.0° higher correction in L4-S1 lordosis ( P =0.012) than L4-L5 TLIF. At the same time, however, L5-S1 TLIF patients experienced significantly higher rates of pseudoarthrosis (8.0% vs 1.6%, P =0.036) and subsequent spine surgery (18.0% vs. 7.2%, P =0.034), specifically for pseudoarthrosis (6.0% vs. 0.0%, P =0.006), with this cohort having 8.7 times higher odds of subsequent spine surgery for pseudoarthrosis ( P =0.015) than L4-L5 TLIF patients on multivariate logistic analyses. PROMs, on the other hand, were not different across the two cohorts. Conclusions. Although L5-S1 TLIF yielded good radiographic correction, it was associated with higher rates of subsequent spine surgery for pseudoarthrosis compared to L4-L5 TLIF. These findings may be related to differences in native segmental alignment and biomechanics across the L4-L5 and L5-S1 motion segments and are important to consider during surgical planning. Level of Evidence. IV.