L5 vs. pelvic fixation as the lowest instrumented vertebra in long-segment fusion for adult spinal deformity: a systematic review and meta-analysis.

PURPOSE: To compare radiographic outcomes, patient-reported outcomes (PROs), and complications between L5 and sacropelvic fixation as the lowest instrumented vertebra (LIV) in long-segment fusion for adult spinal deformity (ASD).

METHODS

Following PRISMA 2020 guidelines, PubMed, Web of Science, Scopus, and Embase were searched for studies comparing L5 vs. pelvic fixation in ASD. Studies with Newcastle-Ottawa Scale (NOS) ≥ 7 were included. Extracted data included demographics, radiographic parameters [pelvic tilt (PT), lumbar lordosis (LL), sagittal vertical axis (SVA)], complications, and PROs [Scoliosis Research Society (SRS) and Oswestry Disability Index (OD)]. Meta-analysis used standardized mean differences (SMD) and odds ratios (OR). Heterogeneity was assessed with I2, and publication bias with Egger's test.

RESULTS

Nine studies (1196 patients; mean age 67.5 years; mean follow-up 36.5 months) were included. Pelvic fixation achieved better sagittal correction: lower PT (SMD 0.88, p = 0.005), higher LL (SMD - 0.76, p < 0.001), and lower SVA (SMD 0.82, p = 0.016). PROs were similar at baseline and follow-up (all p > 0.05). L5 fixation had shorter operative time (SMD - 0.78, p = 0.005) but higher distal junctional failure (DJF) risk (OR 2.62, p = 0.002). Predictors of DJF with L5 LIV included older age, extensive fusion, high pelvic incidence, facet degeneration, and poor baseline sagittal balance.

CONCLUSIONS

Pelvic fixation provides superior sagittal correction with comparable PROs and overall complications, while L5 fixation carries a 2.6-fold higher DJF risk. LIV selection must be individualized; pelvic fixation is strongly recommended for patients with advanced age (> 66 years), high pelvic incidence (> 52°), or severe sagittal malalignment to mitigate mechanical failure. PROSPERO ID Number: CRD420251129518.