The superiority of immune-inflammation summary index for diagnosing periprosthetic joint infection

Background: Accurate and rapid diagnosis of periprosthetic joint infections (PJI) is particularly challenging. This study aimed to evaluate the diagnostic value of a newly developed immune-inflammation summary index (IISI) for PJI.

Methods: Our study enrolled 171 aseptic loosening (AL) and 172 PJI cases. Based on a biological-driven approach, the IISI was formulated as C-reaction protein (CRP) × globulin × neutrophil / [lymphocyte × albumin]. Receiver operating characteristic (ROC) curves were constructed to compare the diagnostic performance of IISI with other known serum markers. Subgroup analysis was also performed to explore the robustness of IISI. Restricted cubic splines were used to evaluate the dose-response association. Additionally, changes in IISI levels prior to reimplantation were investigated.

Results: The levels of all tested biomarkers were significantly different between the PJI and AL groups (all P < 0.05). ROC analysis revealed that IISI outperformed any other marker in diagnosing PJI with an area under the curve (AUC) value of 0.890. The diagnostic performance of IISI was also optimal in the hip (0.898), knee (0.903), low-grade infection (0.841), and culture-negative (0.919) subgroups. The optimal cut-off value is stabilized at around 1.6. The nonlinear association between IISI scores and PJI was also confirmed (P < 0.001). The levels of IISI before reimplantation demonstrated a significant decrease (P < 0.001) and were comparable to those of the AL group (P = 0.143).

Conclusion: IISI can improve the utilization of serum indicators and is superior to other well-known biomarkers in diagnosing PJI. Further studies should evaluate its specific role in different infectious and inflammatory diseases.