This three-institution retrospective cohort study analyzed preoperative synovial fluid aspirates from 429 revision TKA knees to determine evidence-based cutoff values for leukocyte count and neutrophil percentage in diagnosing periprosthetic joint infection, using ROC curve analysis to optimize the balance of sensitivity and specificity.
When working up a painful TKA preoperatively, use >1100 cells/mm³ and >64% neutrophils as your synovial fluid thresholds — if both are above cutoff, infection is confirmed in ~99% of cases; if both are below, you can effectively rule it out.
Remember these cutoffs are invalid in patients with inflammatory arthropathies (RA, gout, SLE), who were explicitly excluded from this study.
This three-institution retrospective cohort study analyzed preoperative synovial fluid aspirates from 429 revision TKA knees to determine evidence-based cutoff values for leukocyte count and neutrophil percentage in diagnosing periprosthetic joint infection, using ROC curve analysis to optimize the balance of sensitivity and specificity.
When working up a painful TKA preoperatively, use >1100 cells/mm³ and >64% neutrophils as your synovial fluid thresholds — if both are above cutoff, infection is confirmed in ~99% of cases; if both are below, you can effectively rule it out.
Remember these cutoffs are invalid in patients with inflammatory arthropathies (RA, gout, SLE), who were explicitly excluded from this study.