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BackgroundPostoperative acute kidney injury (AKI) is a serious complication following orthopedic surgery. Both insulin resistance (IR) and inflammation have been implicated as risk factors for AKI in surgical populations. This study aimed to evaluate the joint association of IR and inflammatory markers for postoperative AKI after orthopedic surgery.MethodsThis retrospective cohort study enrolled 4,665 adult patients undergoing orthopedic surgery at Nanfang Hospital, Southern Medical University, between January 2018 and October 2023. The primary outcome was AKI; secondary outcomes included intensive care unit (ICU) admission and the length of hospital stay after surgery. IR was evaluated using triglyceride-glucose index (TyG) and TyG-body mass index (TyG-BMI), while inflammatory status was assessed by neutrophil-percentage-to-albumin ratio (NPAR). Multivariable logistic regression models and restricted cubic splines were used to estimate AKI risk. Discriminatory ability was assessed through receiver operating characteristic (ROC) curves with area under curves (AUC). Sensitivity analyses were performed by sequentially excluding predefined high-risk subgroups (e.g., spinal/deformity correction, emergency surgery, diabetes, hyperlipemia, acute trauma/infection) and through a best-case scenario analysis assuming missing creatinine values as non-events.ResultsAmong 4,665 patients, 232 (4.97%) developed AKI. In fully adjusted models, both IR indicators and NPAR were linearly associated with an increased risk of AKI. The combination of elevated IR indicators and NPAR demonstrated a significantly stronger association with AKI compared to low levels [odds ratio (OR) and 95% confidence interval (CI): 2.819 (1.749–4.544) for TyG and NPAR; 3.324 (2.022–5.462) for TyG-BMI and NPAR]. The TyG-BMI and NPAR combination yielded superior discrimination ability (AUC: 0.683; 95% CI: 0.648–0.718) compared to either biomarker alone (TyG-BMI AUC: 0.559; NPAR AUC: 0.655). Sensitivity analyses confirmed the robustness of these findings. Additionally, elevated TyG and NPAR were associated with delayed discharge, while elevated TyG-BMI was not. Among the three markers, only NPAR was significantly associated with increased odds of postoperative ICU admission.ConclusionsPreoperative IR indicators and NPAR are independently associated with AKI after orthopedic surgery. The combination of TyG-BMI and NPAR shows improved discrimination for postoperative AKI. Further prospective multi-center studies are warranted to validate these findings.