Preoperative Systemic Inflammatory Response Index (SIRI) as a predictor of early surgical site infection following instrumented lumbar spine surgery.

BACKGROUND

Evaluate the association between preoperative SIRI and early postoperative SSI and to assess its diagnostic performance.

METHODS

Retrospective cohort study was conducted including 500 consecutive adult patients who underwent posterior fusion lumbar spine surgery for degenerative pathology. Preoperative neutrophil, lymphocyte, and monocyte counts were used to calculate SIRI. The primary outcome was early acute deep postoperative SSI. Associations were analyzed using univariate and penalized multivariate logistic regression. Discriminatory performance was assessed using receiver operating characteristic curve analysis.

RESULTS

Early postoperative SSI occurred in 27 patients (5.4%). Patients who developed infection had significantly higher preoperative SIRI values than those without infection (median 1.78 [IQR, 1.02-3.41] vs. 1.12 [IQR, 0.62-2.04]; p = 0.031). In the multivariate logistic regression model, log-transformed SIRI remained independently associated with infection (adjusted OR 1.93; 95% CI 1.02-3.67; p = 0.044). Preoperative SIRI demonstrated moderate discriminatory ability for early SSI, with an AUC of 0.66 (95% CI, 0.54-0.77; p = 0.03). The optimal cutoff value of 1.29 yielded a sensitivity of 63.0% and a specificity of 68.3%.

CONCLUSIONS

Preoperative SIRI is independently associated with early postoperative SSI following instrumented lumbar spine surgery for degenerative pathology. Although its discriminatory performance is moderate, SIRI represents a simple, inexpensive, and readily available adjunctive marker for preoperative risk stratification, particularly useful for identifying patients at low risk of postoperative infection.