Low dose rhBMP-2 use in three- and four-level ACDF without posterior fusion: a comparative analysis and viable...

Pseudarthrosis is a known complication following multilevel anterior cervical discectomy and fusion (ACDF), yet data remain limited on its incidence and risk factors in multilevel procedures in the modern era.

This study aimed to characterize the incidence of pseudarthroses and identify associated risk factors in patients undergoing three- or four-level ACDF procedures without posterior fixation, while also evaluating the potential role of low-dose rhBMP-2 in promoting fusion and supporting anterior-only surgical strategies.

Retrospective single-center observational cohort study.

Two hundred and six patients treated by three- or four-level ACDF.

Radiological records, including independent review of interspinous motion, Cobb angle, bony bridging, and fusion rate, were collected. Surgical-related information and complications were also recorded.

A retrospective review of adults who underwent three- or four-level ACDF with anterior plating between 2011 and 2024 was performed at a single academic institution. Patients were excluded if follow-up imaging was <12 months or if they had a prior cervical procedure, corpectomy, or combined anterior-posterior surgery. Demographic, surgical details, and outcome data were collected. Pseudarthrosis was assessed using dynamic flexion-extension radiographs evaluating interspinous motion and change in Cobb angle. When flexion-extension imaging was not available, fusion status was evaluated using static radiographs and/or computed tomography. The primary outcome measure was fusion status at 1 year. Secondary outcome measures were postoperative complications, readmission, and reoperation rates. Continuous variables were reported as median (interquartile range) and compared using the Wilcoxon rank-sum test. Categorical variables were presented as percentages and compared using Pearson's chi-square or Fisher's exact tests when cell counts were low. Multivariable logistic regression was performed to identify independent predictors of outcome variables.

A total of 206 patients were included (median age 57 [51-66] years; 59.7% female; 66.0% White). Most underwent three-level fusion (85.9%), and recombinant human bone morphogenetic protein (rhBMP-2) was used in 48.5%. In total, pseudarthroses occurred in 28 patients (13.6%), with 13 (6.3%) patients having symptomatic pseudarthrosis. Pseudarthroses occurred in 13.0% (n=23) of three-level constructs versus 17.2% (n=5) of four-level constructs (p=.56). Pseudarthrosis rates did not vary significantly by implant type. Patients with any smoking history had higher pseudarthrosis rates compared with nonsmokers (23.3% vs. 6.7%, p<.001). Among patients with any smoking history, rhBMP-2 was significantly associated with reduced pseudarthrosis incidence (14.0% vs. 36.1%, p=.017). Among all patients, multivariable logistic regression identified rhBMP-2 use as independently protective of pseudarthrosis (odds ratio=0.15, 95% confidence interval 0.04-0.55, p=.004). However, rhBMP-2 was identified as an independent predictor of increased complication rates (odds ratio=2.70, 95% confidence interval 1.01-7.16, p=.047), with transient dysphagia being the most frequent complication (n=15, 93.8%).

Three- and four-level ACDF without posterior fusion demonstrated much lower nonunion rate compared to historic and recently reported rates, with pseudarthroses occurring in 13.6% of patients and symptomatic pseudarthroses occurring in 6.3% of patients. Among all patients, rhBMP-2 use was associated with 6.7-fold lower odds of pseudarthrosis. Smoking history was strongly associated with nonunion, and rhBMP-2 use appeared to mitigate this risk among smokers. These findings support individualized fusion strategies and selective use of biologic augmentation in high-risk patients.