The prognostic nutritional index is an early predictive marker for surgical site infection after spinal fusion surgery: a nested case-control study

OBJECTIVE: This study aimed to evaluate the predictive value of the preoperative prognostic nutritional index (PNI) for surgical site infection (SSI) following spinal fusion surgery and validate its clinical utility as a simple screening tool. METHODS: A retrospective nested case-control study was conducted on consecutive patients who underwent spinal fusion surgery between October 2014 and October 2024. A total of 220 patients with SSI (cases) were matched with 440 SSI-free patients (controls) by age, sex, and calendar year. Preoperative PNI was calculated based on serum albumin concentration and total peripheral blood lymphocyte count. Conditional logistic regression models were used to assess the independent association between PNI and SSI, with subgroup analyses stratified by disease category (degenerative diseases or spinal deformity). RESULTS: The proportion of patients with PNI < 50 was significantly higher in cases than in controls (34.5% vs. 22.7%, P = 0.001). Univariate analysis showed that PNI < 50 was associated with an increased SSI risk (OR = 1.794, 95%CI = 1.257-2.562, P = 0.001). After adjusting for confounding factors including diabetes status, estimated blood loss, duration of surgery, drain length, number of surgical levels, surgical region, body mass index, age-adjusted Charlson comorbidity index, and American Society of Anesthesiologists physical status classification, PNI < 50 remained an independent predictor of SSI (OR = 1.568, 95%CI = 1.070-2.298, P = 0.021). Subgroup analysis revealed that the predictive value of PNI was significant in patients with degenerative spinal diseases (OR = 1.814, 95%CI = 1.042-3.156, P = 0.035) but not in those with spinal deformity (P > 0.05). CONCLUSION: Preoperative PNI < 50 is an independent early predictive marker for SSI after spinal fusion surgery, particularly in patients with degenerative spinal diseases. Routine PNI assessment can facilitate preoperative risk stratification and individualized infection prevention strategies, improving surgical outcomes.