Association between preoperative controlling nutritional status score and surgical site infection following instrumented posterior lumbar interbody fusion

Objective This study aimed to investigate the association between preoperative Controlling Nutritional Status (CONUT) score and surgical site infection (SSI) after instrumented posterior lumbar interbody fusion (PLIF). Methods This retrospective cohort study included patients who underwent instrumented PLIF for lumbar degenerative disease at our institution between January 2021 and March 2025. SSI events within 12 months postoperatively were identified through medical records and follow-up assessment. Restricted cubic spline (RCS) analysis was performed to evaluate the potential nonlinear association between CONUT score and SSI risk. Based on the observed risk pattern and clinical interpretability, an exploratory cutoff of 3 was used to dichotomize patients for categorical analysis. Multivariable logistic regression was performed to assess the independent association between CONUT score and SSI, with sensitivity analysis treating CONUT as a continuous variable. Results Among 1,414 patients included, 43 (3.0%) developed SSI within 12 months postoperatively. RCS analysis suggested a significant nonlinear association between CONUT score and SSI risk ( P for nonlinearity = 0.015), with risk beginning to increase at approximately a CONUT score of 3. Patients were dichotomized into CONUT < 3 and ≥3 groups. After adjustment for potential confounders, CONUT ≥3 was independently associated with an increased risk of SSI (OR, 2.49; 95% CI, 1.32–4.70; P = 0.005). Sensitivity analysis showed that each 1-point increase in CONUT score was associated with a 28% increase in SSI risk (OR, 1.28; 95% CI, 1.12–1.45; P < 0.001). Conclusion Higher preoperative CONUT score was independently associated with increased SSI risk after instrumented PLIF. Given its accessibility and low cost, CONUT may serve as a practical indicator for preoperative nutritional assessment and SSI risk stratification, although further external validation is warranted.