Is extension of multi-level lumbar fusion to S1 necessary in the absence of L5-S1 instability? A comparative study of selective decompression versus TLIF with S1 pedicle screw fixation.

BACKGROUND: S1 pedicle screw loosening remains a clinically significant complication in lumbosacral fusion, with reported incidences ranging from 15.6% to 41.9%. In patients undergoing multi-level posterior lumbar fusion with concomitant symptomatic but stable L5-S1 pathology, it remains unclear whether extending the construct to the sacrum is necessary. METHODS: This retrospective study included 60 patients who underwent multi-level posterior lumbar instrumentation (fusion constructs spanning 2-4 segments) between November 2023 and April 2024. All patients had symptomatic L5-S1 pathology (disc herniation or stenosis) without radiographic instability, and required fusion for upper lumbar pathology. Patients with L5-S1 instability (>3 mm translation or >10° angulation on flexion-extension radiographs) were excluded. Group 1 (n = 30) underwent selective L5-S1 decompression without S1 fixation; Group 2 (n = 30) underwent TLIF with S1 pedicle screw instrumentation. Clinical outcomes (ODI and VAS), perioperative parameters, and complications were evaluated at 1, 6, and 24 months. RESULTS: Groups were comparable at baseline. Operative time (148.4 ± 26.1 vs. 204.7 ± 32.8 min, p < 0.001), estimated blood loss (376.7 ± 114.3 vs. 653.3 ± 211.8 mL, p < 0.001), and hospital stay (3.7 ± 0.9 vs. 4.4 ± 0.8 days, p = 0.004) were significantly lower in Group 1. Both groups demonstrated significant within-group improvements in ODI and VAS scores at all time points (p < 0.001). No statistically significant between-group differences were observed in ODI or VAS at 6 months or 24 months. Group 1 showed significantly lower VAS at 1 month (p = 0.022). Radiographic S1 screw loosening was observed in 7 of 30 patients (23.3%) in Group 2. CONCLUSION: In this retrospective cohort, selective decompression of the L5-S1 segment without S1 instrumentation was associated with comparable mid-term clinical outcomes while reducing operative time, blood loss, and S1 screw-related complications.