The Enlarged Lymph Node Ratio Performs Well for Diagnosing Periprosthetic Joint Infection After Total Hip Arthroplasty.

BACKGROUND

The aim of this study was to evaluate the predictive value of the enlarged lymph node ratio (ELNR) derived from regional lymph nodes (LNs) for periprosthetic joint infection (PJI) following total hip arthroplasty.

METHODS

We retrospectively reviewed the medical records of patients who underwent revision total hip arthroplasty between January 2015 and February 2025. Using the 2013 Musculoskeletal Infection Society (MSIS) criteria, 59 cases of PJI and 59 matched controls with aseptic loosening were enrolled. The primary variables, including ELNR, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR), were dichotomized using cutoff values determined by the maximal Youden index. Multivariate analyses were then performed to develop two combined diagnostic models: (1) CRP plus ESR and (2) CRP plus ESR plus ELNR. Receiver operating characteristic (ROC) curves for ELNR, CRP, ESR, CRP plus ESR, and CRP plus ESR plus ELNR were generated, and the corresponding areas under the curve (AUC) were obtained.

RESULTS

There were significant statistical differences in ELNR, CRP, and ESR levels between the PJI cohort and the aseptic loosening control group (P < 0.001). Multivariate regression analysis confirmed ELNR, CRP, and ESR as independent predictors of PJI. The ELNR achieved an AUC of 0.797, with an optimal cutoff value of 0.11, yielding a sensitivity of 69.5% and a specificity of 89.8%. The CRP plus ESR plus ELNR model demonstrated an AUC of 0.919, which was significantly higher than that of each individual parameter (all P < 0.001); however, it did not differ significantly from the CRP plus ESR model. Notably, the CRP plus ESR plus ELNR model exhibited higher sensitivity than CRP plus ESR (F = 4; P = 0.043, McNemar's test), indicating that the inclusion of ELNR enhanced diagnostic performance.

CONCLUSIONS

The ELNR is a promising diagnostic indicator for PJI, which could enhance diagnostic accuracy when combined with CRP and ESR and thereby aid in the early identification and management of PJI.