Risk factors for surgical site infection following spinal instrumentation surgery

In spinal instrumentation surgeries, surgical site infection (SSI) is one of the complications to be avoided. However, spinal instrumentation surgeries have a higher rate of SSI than other clean orthopedic surgeries. The purpose of this study was to investigate the risk factors for SSI following spinal instrumentation surgeries and contribute to the prevention of SSIs by identifying high-risk patients.

Records of 431 patients who underwent spinal instrumentation surgeries from 2011 to 2014 with a minimum follow-up period of 90 days were retrospectively reviewed. Associations of SSI with various preoperative, operative, and postoperative factors were statistically analyzed with univariate and stepwise multivariate logistic regression analysis.

Deep or superficial SSIs were observed in 15 patients (3.5%). Univariate analysis revealed significant association of SSI with diabetes mellitus (odds ratio [OR] 4.7, 95% confidence interval [CI] 1.5-14.4; p = 0.012) and serum albumin ≤3.5 g/dl (OR 3.35, 95% CI 1.1-10.38, p = 0.012). The number of regular medications prescribed in patients with SSI (8.2 ± 5.4) was significantly more than that in patients without SSI (3.8 ± 4.4) (p = 0.001), and the cut-off value of the number of medications was 7, as derived from receiver operating characteristics analysis. Multivariate analysis revealed that the number of regular medications ≥7 was an independent risk factor significantly associated with SSIs (OR 7.3, 95% CI 2.3-24.0, p = 0.001).

Our study demonstrated that an important risk factor for SSI after spinal instrumentation surgery was number of regular medications ≥7. Number of regular medications is a simple and valuable risk index for SSI, which reflects the influence of medications and comorbidities.