Postoperative inflammatory markers and surgical wound infection after elective short-segment lumbar fusion: the...

Introduction: Postoperative white blood cell (WBC) count and neutrophil-to-lymphocyte ratio (NLR) are routinely available after lumbar fusion, but early elevations may reflect surgical stress. We evaluated associations of postoperative day (POD) 1 and POD3 WBC/NLR with 90 d surgical wound infection (SWI) after elective short-segment lumbar fusion. Methods: This retrospective cohort included adults undergoing elective one- to three-level lumbar fusion from 2022 to 2024 at one academic center. SWI was a pragmatic electronic-health-record-based endpoint encompassing clinically documented wound-related events, not a uniformly culture-confirmed deep, implant-associated, or surveillance-defined infection. Complete-case univariable and parsimoniously adjusted logistic regressions examined WBC/NLR associations with SWI. Results: Among 380 outcome-eligible patients, 18 (4.7 %) developed SWI. POD1 analyses included 368 patients (18 events), POD3 analyses 336 (17 events), and paired analyses 327 (17 events). After adjustment for body mass index and operative duration, POD1 associations were attenuated; POD3 WBC (odds ratio 1.17, 95 % confidence interval 1.00-1.37; $p=0.049$ ) and NLR (odds ratio 1.12, 95 % confidence interval 1.01-1.23; $p=0.026$ ) remained associated with SWI. However, these associations weakened after adjustment for corresponding POD1 values. Absolute and percentage POD1-to-POD3 changes were not significantly associated with SWI. Conclusions: POD1 WBC/NLR elevations were associated with patient and operative context. POD3 values showed exploratory associations with SWI after limited adjustment but did not establish diagnostic thresholds, clinical utility, or a validated prediction model.