Objectives: It is controversial whether to stop the fusion at L5 or S1 in adult spinal deformity (ASD) surgery. Our hypothesis is that we can stop long fusion at L5 for selected patients with less severe disability and less complex deformity. Aim was to compare minimum 5-year outcomes between ASD patients with fusion to L5 versus S1.
Patients and methods: Consecutive 40 patients (≥50 years of age) with ASD underwent spinal fusion from lower thoracic spine to L5 or S1 between 2008 and 2011. 33 patients (82.5 %) had a minimum 5-year follow-up. Lower instrumented vertebra (LIV) was L5 in 12 patients (L5 group) and S1 in 21 (S1 group). Clinical and radiographical parameters were compared between L5 and S1 group.
Results: There were statistically significant differences between two groups (L5 vs S1) in %male (50 % vs 14 %), %type-N of SRS-Schwab classification (83 % vs 38 %), preop ODI (40.5 vs 56), correction loss of LL (11˚ vs 3˚), final TK (32˚ vs 50˚), correction loss of TK (-1˚ vs 17˚), final improvement of PT (3˚ vs 10˚), final improvement of PI-LL (26˚ vs 39˚), PJK (8% vs 48 %), and revision surgery rate (50 % vs 14 %). Causes of revision surgery in L5 group were distal junctional failure in 5 patients and foraminal stenosis at L5-S1 in 1. All of them underwent additional spinal fusion to the sacrum. Whereas, causes of revision surgery in S1 group were rod fracture in 2 patients and proximal junctional failure in 1.
Conclusion: Although fusion to L5 was conducted for selected ASD patients with less severe disability (better ODI) and less complex deformity (type N), 50 % of the patients required additional fusion to the pelvis. Decision making to stop the long fusion at L5 for ASD patients ≥50 years of age should be made with careful considerations.
Keywords: Adjacent segment disease; Adult spinal deformity; L5-S1 segment; Long fusion; Revision surgery; Spinopelvic fusion.
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