• Wen Wei Gerard Ee, Wen Liang Joel Lau, William Yeo, Yap Von Bing, and Wai Mun Yue.
• Department of Orthopaedics, Singapore General Hospital, Outram Road, Singapore, 169 608, Singapore, gerardee@gmail.com.
• Clin. Orthop. Relat. Res. 2014 Jun 1;472(6):1718-24.

BackgroundSurgical site infection (SSI) ranges from 1.9% to 5.5% in most large series. Minimally invasive surgery (MIS) has been postulated to reduce SSI rates.Questions/Purposes(1) Is MIS associated with a lower incidence of SSI compared with open spinal surgery? (2) Are there other independent risk factors associated with SSI? (3) What bacteria are most common in spinal SSI?MethodsMedical records of 2299 patients who underwent transforaminal lumbar interbody fusion, laminectomy, or discectomy were analyzed and selected for a nested case-control analysis. Twenty-seven cases with SSI were matched with 162 control subjects without SSI stratified based on procedure performed within 28 days of the case's date of surgery. Patients were identified from an institutional database at a tertiary care hospital. MIS involved spinal procedures performed through a tubular retractor system. Univariate and multivariate analyses were performed.ResultsPatients undergoing open spinal surgery were 5.77 times more likely to develop SSI compared with MIS approaches (odds ratio [OR], 5.77; 95% confidence interval [CI], 1.0-32.7; p = 0.048). Also, from the multivariate regression model, diabetes (OR, 4.7; 95% CI, 1.3-17.0; p = 0.018), number of levels operated on (OR, 3.5; 95% CI, 1.6-7.5; p = 0.001), and body mass index (OR, 1.2; 95% CI, 1.0-1.3; p = 0.010) were predictive of an increased risk in SSI. Staphylococcus aureus was most frequently identified, being present in 12 of 21 (52.4%) patients in whom positive cultures were obtained. Four of the 12 patients had methicillin-resistant S aureus infection.ConclusionsIn our series, MIS has a lower incidence of SSI. The risk factors predictive of SSI should be further evaluated in well-designed prospective trials.Level Of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

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