The Fate of L5–S1 with Low Dose BMP-2 and Pelvic Fixation in Adult Deformity Surgery

Abstract

Introduction Pseudarthrosis at L5–S1 is one of the most common complications of long fusions to the sacrum in adult deformity surgery. Strategies for decreasing pseudarthrosis include interbody fusion, use of BMP-2 at the lumbosacral junction, and the use of sacropelvic fixation, individually or in combination. High-dose BMP-2 (20–40 mg) placed posterolaterally has shown comparable fusion rates to interbody fusion. The purpose of this study was to evaluate L5–S1 fusion rates when lower dose BMP-2 (average 3.2 mg) and pelvic fixation were used, with or without interbody fusion. Materials and Methods This is a retrospective review of 61 consecutive patients with a minimum follow-up of 2 years at a single institution. All patients had an isolated posterior approach, ≥ 5 levels fused including L5–S1, use of pelvic fixation, and no previous L5–S1 procedures. The patients were divided into two groups for comparison based on the use of an interbody cage/fusion at the L5–S1 level. Radiographic union was assessed by three independent reviewers using Bridwell criteria. Revision rates and implant-related complications were also reported. Results The fusion rate at L5–S1 was 97% (59/61) with no difference between the interbody and no interbody fusion groups (97 vs. 96%, p = 1.0). The overall revision rate for L5–S1 nonunion was 1.6%. The mean amount of BMP-2 used in the interbody group was 4.1 mg (2–10), 2.5 mg (0–8) in the disc space, and 1.6 mg (0–4) in the interbody cage, while there was no difference in the amount of rhBMP-2 placed posterolaterally between the two groups (IF = 1.6 vs. NIF = 2.0 mg, p = 0.08) along with autograft and allograft. There were no significant differences in the radiographic parameters or deformity correction between the groups. Conclusion The use of low dose of BMP-2 at the L5–S1 level in combination with sacropelvic fixation achieved satisfactory outcomes in adult deformity surgery. No additional radiologic or clinical benefit was realized with the addition of an interbody fusion at the L5–S1 level.