39. Risk factors for sacroiliac joint fusion after instrumented spinal fusion

Abstract

BACKGROUND CONTEXT

Chronic back pain after a spinal fusion is multifactorial, but one factor is the development of adjacent segment disease, which occurs at a pooled annual incidence of about 2% a year. Fusion constructs extending to the sacrum increase angular motion and stress across the sacroiliac (SI) joint, which can lead to accelerated degeneration of the joint. The rate of SI joint degeneration after lumbar/lumbosacral fusion has been reported in one prospective study to be upwards of 75%, which was significantly higher than the control group of 38.2%. Because of the high incidence of degeneration after spinal fusions, some surgeons advocate for simultaneous SI joint fusion at the time of the primary spinal fusion. In a retrospective analysis of a prospectively maintained database, none of the patients undergoing simultaneous SI joint fusion with spinal fusion experienced postoperative SI joint pain, while 44.6% of those without simultaneous SI joint fusion did develop such pain. However, most studies have been institution-specific reporting and subsequent systematic reviews. There has been no large-scale database study looking at the risk factors for future SI joint fusion after spinal fusion.

PURPOSE

To identify risk factors for SI joint fusion after instrumented spinal fusion.

STUDY DESIGN/SETTING

Retrospective cohort study.

PATIENT SAMPLE

PearlDiver BiscayneBay database.

OUTCOME MEASURES

Odds ratios.

METHODS

Patients were identified from the PearlDiver BiscayneBay database (Colorado Springs, CO, USA). Patients who underwent 1-level (CPT: 22840), 3-6-level (22842), and 7-13-level posterior spinal instrumentation (22843 and 22844) were identified, excluding patients with fusions in the cervical spine (22595 and 22600). Patients were separated based on whether or not they received an SI joint fusion after their spinal fusion (27280 and 27279). The following patient factors and their association with future SI joint fusion were evaluated: age, gender, obesity, fibromyalgia, diabetes, tobacco use, prior SI joint injection, and spinal fusion length. A logistic regression as well as a machine learning logistic regression model was performed to evaluate the associations between patient factors and incidence of SI joint fusion.

RESULTS

A total of 539,042 patients underwent posterior instrumentation with 5981 patients also undergoing SI joint fusion at a later date. Factors associated with future SI joint fusion included female gender, patients with obesity, fibromyalgia, diabetes, tobacco use, and prior SI joint injection. Construct lengths of 3-6 and 7-13 were statistically associated with the patient undergoing future SI joint fusion. Prior SI joint injection had the highest odds ratio for undergoing future SI joint fusion (OR: 8.73; 95% CI: 8.28-9.20), followed by 7-13 level fusion (OR: 2.59; 95% CI: 2.40-2.78) and 3-6 level fusion (OR: 1.49; 95% CI: 1.41-1.57). There was no significant differences in age between those who would undergo SI joint fusion and those who did not. A logistic regression was performed which showed that prior SI joint fusion (OR: 8.14; 97.5% CI: 7.71-8.59), 7-13 level fusion (OR: 3.76; 97.5% CI: 3.48-4.07), and 3-6 level fusion (OR: 1.54; 97.5% CI: 1.46-1.62) were most associated with future SI joint fusion. Our machine learning logistic regression model (Accuracy: 81.7%, Sensitivity: 60.1%, Specificity: 82.0%) found that prior SI joint fusion was most closely associated with prior SI joint injection, followed by 7-13 level fusion and 3-6 level fusion. A Charleston Comorbidity Index of 4 or more and diabetes were slightly predictive of no future SI joint fusion.

CONCLUSIONS

Our study found that the highest predictor of requiring subsequent SI joint fusion after spinal fusion is a prior SI joint injection. We also found that longer constructs were associated with increased risk for future SI joint fusion. This is the first large scale database study to be performed looking at risk factors for future SI joint fusion after spinal fusion. These results help aid surgeons in assessing the risk of future SI joint fusion and the potential need for a concomitant procedure.

FDA Device/Drug Status

This abstract does not discuss or include any applicable devices or drugs.