Paper of the Week: Risk Factors for Acute Surgical Site Infection after Spinal Instrumentation Procedures: A Case-Control Study

Tiago Amorim-Barbosa, Ricardo Sousa, Ricardo Rodrigues-Pinto and António Oliveira

Int J Spine Surg. 2021;8130
doi: 10.14444/8130

Summary by Khoa Tran, BA

Surgical site infection (SSI) is a major concern in spine surgery, resulting in increased rates of morbidity, mortality, and health care costs and requiring surgical debridement, long-term antibiotics, and hardware removal [1]. The reported prevalence of SSI ranges from 0.7%-12.0%, depending on the surgical indication and type of procedure [2-4]. In order to reduce the incidence of SSIs and improve overall outcomes for patients, it is important to first identify risk factors for their occurrence.

Amorim-Barbosa et al. conducted a case-control study on 2,582 patients who underwent lumbar spinal instrumentation between January 2009 and August 2017. The primary outcome was identifying patient- and surgery-related risk factors associated with spinal fusion SSI. Patients were categorized into 3 groups: (1) fusion for lumbar spinal degenerative diseases; (2) spinal instrumentation/fusion for fractures; and (3) fusion for pediatric spinal deformity. Positive SSI cases were identified by positive wound culture reports and readmissions with a minimum 1-year follow-up. Each positive patient case was matched with a control of the same preoperative diagnosis in a 1:2 ratio.

In total, 33 positive SSI cases were identified from the cohort: 14 (out of 1,326) in the degenerative group, 11 (out of 207) in the trauma group, and 8 (out of 850) in the pediatric spinal deformity group. Multivariate analysis showed procedure duration was a statistically significant independent risk factor for SSI in degenerative and traumatic spine surgery. Each additional hour of surgery doubling the risk for SSI in the degenerative group (OR 2.23; 95% CI 1.03–4.82), whereas in the trauma group, each additional hour poses almost a fourfold higher risk for SSI (OR 3.79; 95% CI 1.27–11.32). Analysis also found a supplemental level of instrumentation as an independent risk factor in trauma spine surgery, demonstrating a 12-fold increased risk for SSI (OR 11.77; 95% CI 1.55–89.40). In the pediatric deformity group, there were no statistically significant results found in multivariate analysis.

The authors concluded that procedure duration is a risk factor for SSI after spinal instrumentation in degenerative and traumatic spine surgery. In addition, number of levels instrumented was an additional risk factor in trauma spine surgery. These findings were limited by its retrospective nature as accuracy of the data was dependent on documentation inserted into electronic and paper medical records. Because this was a single-institution study, the dataset was limited, and the lack of significance of some parameters may reflect insufficient statistical power.


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  2. Fang A, Hu SS, Endres N, Bradford DS. Risk factors for infection after spinal surgery. Spine (Phila Pa 1976). 2005;30(12):1460–1465.
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