In the setting of a PPF, the diagnosis of PJI becomes even more complex: The sensitivity of the currently recommended parameters for PJI like serum C-reactive Protein (CRP) or synovial white blood cell count (WBC) decreases, because a PPF causes a hemarthrosis with a subsequent local inflammatory response, which may confound synovial analyses15. The gene discussed is CRP; the disease is juvenile polyposis syndrome.