The synovial fluid IL-1β cutoff value of 312.7 pg/mL had sensitivity of 97.3% (95% CI, 85.8%–99.9%), specificity of 94.64% (95% CI, 85.1%–98.9%), and accuracy of 95.7% for detecting chronic PJI, with high NPV of 98.15% and high PPV of 92.31%. This evidence concerns the gene IL1B and juvenile polyposis syndrome.