Can the Leukocyte Esterase Strip Test Predict Persistence of Periprosthetic Joint Infection at Second-Stage Reimplantation?

BACKGROUND: We evaluated the reliability of intraoperative assessment of leukocyte esterase (LE) in synovial fluid samples from patients undergoing reimplantation following implant removal and spacer insertion for periprosthetic joint infection (PJI). Our hypothesis was that a positive intraoperative LE test would be a better predictor of persistent infection than either serum C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) or the combination of serum CRP and ESR. METHODS: The records of 76 patients who received a 2-stage exchange for PJI were retrospectively reviewed. Synovial fluid was collected for LE measurement during surgery before arthrotomy in 79 procedures. Receiver operating characteristic curves were generated. Sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and area under the curve (AUC) of LE, CRP, ESR, and CRP + ESR were calculated. RESULTS: Sensitivity, specificity, positive predictive value, and negative predictive value of the LE assay were 82%, 99%, 90%, and 97%, respectively. Receiver operating characteristic analysis revealed an LE threshold of 1.5 between the first (negative) and the second (positive) level of the ordinal variable, so that a grade starting from 1+ was accurate for a diagnosis of persistent infection (AUC 0.9044). The best thresholds for the CRP and the ESR assay were 8.25 mg/L (82% sensitivity, 84% specificity, AUC 0.8416) and 45 mm/h (55% sensitivity, 87% specificity, AUC 0.7493), respectively. CONCLUSION: The LE strip test proved a reliable tool to diagnose persistence of infection and outperformed the serum CRP and ESR assays. The strip test provides a valuable intraoperative diagnostic during second-stage revision for PJI.

Value of digital telethermography for the diagnosis of septic knee prosthesis: a prospective cohort study.

BACKGROUND: Diagnosis of peri-prosthetic infection remains challenging, often requiring a combination of different tests. METHODS: In this prospective, case-control study, the diagnostic accuracy of telethermography was evaluated in a group of seventy patients who had had a total knee replacement and were undergoing a reoperation because of infection or another implant-related problem, after a minimum of one year from implant. RESULTS: An average differential temperature of the affected versus not affected knee of 1.9 °C was observed in infected prosthesis, compared to 0.3 °C in aseptic failures. Considering a normal reference value equal or less than 1.0 °C, telethermography showed an accuracy, sensitivity, specificity, positive and negative predictive value of, respectively: 0.90, 0.89, 0.91, 0.91, 0.88. CONCLUSIONS: Digital telethermography is a reliable option for diagnosing peri-prosthetic knee infection.