Does Interbody Placement Improve Long-Term Outcomes in Patients Undergoing Single-Level Lumbar Decompression and Fusion for Spondylolisthesis?

Introduction: The impact of interbody placement on spondylolisthesis reduction and lordosis in open, lumbar decompression/fusion for degenerative spondylolisthesis remains understudied. In elective, single-level decompression/fusion for spondylolisthesis, we aimed to evaluate the impact of interbody placement on 1) spondylolisthesis reduction, 2) lumbar and segmental lordosis, 3) reoperation, and 4) patient-reported outcome metrics (PROMs)

Methods: This single-institution, retrospective cohort study included patients undergoing primary, elective, open, single-level lumbar decompression/fusion for spondylolisthesis from 2010-21. The primary exposure variable was interbody placement, with primary outcomes of spondylolisthesis reduction, segmental lordosis, reoperation, and PROMs. Descriptive and univariate/multivariable analysis was performed.

Results: Among 339 patients with a mean follow-up of 6.0±3.0 years, mean age of 63.0±10.9, and 126 (37.2%) males, interbody was placed in 222 (65.5%) patients; 90% of patients had grade 1 spondylolisthesis, 9.4% grade 2, and 0.6% grade 3.

Spondylolisthesis reduction: A 2 mm reduction was seen in 161 (47.5%), with complete reduction in 16 (4.7%). Spondylolisthesis improvement was similar between interbody and non-interbody groups (51.4% vs. 40.2%,p=0.050), with no significant difference in mean improvement (5.6±4.4 mm vs. 5.2±4.7 mm, p=0.463).

Lumbar lordosis: Postoperative lumbar and segmental lordosis were 46.8±13.0º and 19.6±8.1º, respectively, with improvement (>5°) seen in 105 (31.0%) and 118 (34.8%), respectively. No significant difference was found between patients with/without interbody in postoperative segmental lordosis (19.4±8.1º vs. 19.9±8.1º,p=0.614), segmental lordosis correction (0.0±10.7º vs. 0.9±11.4º,p=0.501), lumbar lordosis (45.8±12.8º vs. 48.6±13.2º,p=0.057) or lumbar lordosis correction (1.1±10.1º vs. 1.0±9.2º,p=0.933).

When looking at the impact of year of surgery, it was not associated with improved rate of spondylolisthesis reduction (OR=0.95, 95%CI=0.88-1.02,p=0.128), lumbar lordosis (OR=0.96, 95%CI=0.89-1.03,p=0.260) or segmental lordosis (OR=0.97, 95%CI=0.90-1.04,p=0.368) improvement.

Reoperation and PROMs: Reoperation was performed in 41 (12.1%) patients. No significant difference was found in reoperation (11.3% vs. 13.7%,p=0.517) and PROMs between patients without or with interbody.

Conclusion : In patients undergoing elective, primary, single-level lumbar decompression and fusion for spondylolisthesis, no significant association was found between an interbody placement and the amount of spondylolisthesis reduction, lumbar lordosis, segmental lordosis, reoperation, or PROMs.