The role of immune-inflammatory biomarkers in diagnosing infected nonunion among nonunion patients after repair of extremity fractures

We aimed to assess the diagnostic accuracy of various biomarkers, such as the systemic immune-inflammation index (SII), inflammatory burden index (IBI), pan-immune inflammation value (PIV), and systemic inflammatory response index (SIRI), in cases of infected nonunion after repair of extremity fractures. In this retrospective analysis of patients who underwent internal fixation surgery with open reduction for extremity fractures between January 2015 and June 2024, the following information was evaluated at admission: age, sex, clinical features, erythrocyte sedimentation rate (ESR), white blood cell (WBC) count, platelet count (PC), C-reactive protein (CRP) level, monocyte count (MC), lymphocyte count (LC), neutrophil count (NC), monocyte-lymphocyte ratio (MLR), neutrophil-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), SII, IBI, SIRI, and PIV. Receiver operating characteristic (ROC) curves, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were constructed to compare the diagnostic performance of SII, IBI, SIRI, and PIV with other known serum markers. The study population consisted of 279 patients, of which 66 (23.7%) showed infected nonunion on the basis of the FRI consensus definition. All blood biomarkers were significantly different in patients with infected nonunion than in those with aseptic nonunion ( p < 0.01). ROC analysis revealed that SII, PIV, IBI, and SIRI outperformed any other marker in diagnosing infected nonunion with the area under the curve (AUC) values more than 0.8. PIV showed the highest AUC value (0.823; 95% CI: 0.764–0.882), the highest sensitivity, specificity, and NPV (86.36%, 73.71% and 94.58%, respectively), and an optimal cutoff value of > 532.35. IBI had the highest LR+ with 3.84. PIV had the lowest LR- with 0.19. The SII, PIV, IBI, and SIRI showed potential for diagnosing infected nonunion. Whether SII, PIV, IBI, and SIRI can be regarded as a promising diagnostic indicator requires more studies.