Risk Factors for Sacroiliac Joint Fusion after Instrumented Spinal Fusion.

Study design: Retrospective Cohort Study.

Objective: To identify risk factors for sacroiliac (SI) joint fusion after instrumented spinal fusion.

Methods: Patients were identified from the PearlDiver BiscayneBay database. Patients who underwent 1 level (CPT: 22840), 3-6 vertebral segment (22842), and 7+ vertebral segment spinal fusions (22843 and 22844) were identified. Patients were separated based on whether they received an SI joint fusion (27280 and 27279) after their spinal fusion. A univariate analysis and multivariate logistic regression was performed to evaluate the associations between patient factors and incidence of SI joint fusion.

Results: 549,625 patients who underwent posterior spinal fusions were identified, 6068 of whom underwent subsequent SI joint fusion (1.1%). Factors associated with future SI joint fusion included female gender, patients with obesity, fibromyalgia, diabetes, tobacco use, increased construct length, and prior SI joint injection. Prior SI joint injection had the highest odds ratio (OR: 8.70; 95% CI: 8.25-9.16; P < 0.001), followed by 7+ vertebral segment (OR: 2.17; 95% CI: 2.03-2.33; P < 0.001) and 3-6 vertebral segment fusion (OR: 1.49; 95% CI: 1.42-1.57; P < 0.001).

Conclusions: The highest predictor of requiring subsequent SI joint fusion is a prior SI joint injection. We also found that longer fusion constructs are associated with increased risk for future SI joint fusion.