Correlation of Novel Inflammation Index with Postoperative Acute Kidney Injury in Patients with Joint Arthroplasty: A Retrospective Cohort Study

Background: Acute kidney injury (AKI) is a frequent complication following joint arthroplasty. This study investigated the association between novel inflammation indices and postoperative AKI. Methods: This retrospective cohort study included 1434 patients who underwent hip or knee arthroplasty, with 1225 patients comprising the complete case analysis dataset. The primary analysis was performed using the complete case analysis dataset, while sensitivity analyses were conducted in both the imputed dataset and the dataset excluding patients with abnormal preoperative creatinine. Inflammation indices, including the Systemic Immune-Inflammation Index (SII), Systemic Inflammatory Response Index (SIRI), Aggregate Index of Systemic Inflammation (AISI), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR), were derived from neutrophil, lymphocyte, monocyte, and platelet counts. Multivariate logistic regression and receiver-operating characteristic curve (ROC) analyses were performed to assess predictive performance. The area under the ROC (AUC) was compared using DeLong test. Results: Among 1225 patients in the complete case analysis dataset, 116 (9.47%) developed AKI (Stage I: 59, Stage II: 55, Stage III: 2). Elevated SIRI and MLR were independently associated with increased AKI risk [adjusted OR (95% CI) for Quartile 4 vs Quartile 1: 1.961 (1.070- 3.595) and 1.902 (1.043- 3.468), respectively]. AISI showed marginal significance [adjusted trend OR (95% CI): 1.192 (0.995- 1.428)]. The predictive performance of the basic model (AUC = 0.565) significantly improved after incorporating SIRI, AISI, and MLR (Delta AUC: +0.066, +0.065, +0.070, respectively; all DeLong P < 0.05). Monocyte count alone also enhanced prediction (Delta AUC: +0.065, DeLong P < 0.05). Sensitivity analyses confirmed robustness. Conclusion: SIRI, MLR, AISI, and monocyte count may serve as predictive indicators for AKI following joint arthroplasty. Further randomized trials are needed to establish causality.