Computed Tomography Assessment of Long-Term Fusion and Subsidence for Anterior Lumbar Interbody Fusion Performed at the Lumbosacral Junction.

Study design: Retrospective cohort study.

Objective: To evaluate factors associated with long-term pseudoarthrosis and subsidence following L5-S1 anterior lumbar interbody fusion (ALIF).

Summary of background data: Reported fusion rates for ALIF at the lumbosacral junction vary widely.

Methods: Patients undergoing L5-S1 ALIF (November 1, 2016-September 3, 2021) were retrospectively analyzed. Fusion (Bridwell grades: 1-2) or pseudoarthrosis (Bridwell grades: 3-4) and subsidence (Marchi grades: 0-3) were determined using 1-year follow-up computed tomography (CT) studies.

Results: Overall, 101 patients were analyzed [mean (SD) age, 62.8 (13.3) y; 51 (50.5%) men]. Bone morphogenic protein (BMP) was used in 59 patients (58.4%), demineralized bone matrix in 44 (43.6%), and cellular allograft in 57 (56.4%). Oswestry Disability Index and Short-Form 36 scores improved postoperatively ( P ≤0.01). At L5-S1, 79 patients (78.2%) had fusion at 1 year. Patients receiving 3D-printed porous [89.5% (17/19)] and solid titanium [100% (14/14)] interbody cages were significantly more likely to have fusion than those receiving polyetheretherketone [70.6% (48/68)] interbody cages ( P =0.02). Adjusted multivariate analyses found that titanium interbody cages were associated with fusion (odds ratio=5.42, P =0.04). Patients with subsidence [n=17 (16.8%)] were significantly older than patients without subsidence [n=84 (83.2%)]: 70.2 (4.7) years vs. 61.3 (14.0) years ( P <0.001).

Conclusions: The 1-year postoperative CT findings showed that 78.2% of the cohort achieved fusion. Fusion was more common among patients with 3D-printed and solid titanium implants than among those with polyetheretherketone implants. Subsidence was more common among older patients. No differences in fusion or subsidence were found based on surgical indication, allograft type, or other patient characteristics.