F: 2 positive intraoperative cultures with growth of the same microorganism, as judged by phenotypic characters, were diagnostic for a PJI (Atkins et al. 1998, Mikkelsen et al. 2006, Trampuz et al. 2007, Schafer et al. 2008). A single positive culture or 2 positive cultures revealing different microorganisms (or different phenotypes) with the presence of purulence or a positive culture from joint fluid aspiration were diagnostic for a PJI (Atkins et al. 1998, Zimmerli et al. 2004, Trampuz et al. 2007, Schafer et al. 2008). If none of the cultures were positive, the likelihood of infection was considered to be low (Kamme and Lindberg 1981, Atkins et al. 1998, Mikkelsen et al. 2006, Trampuz et al. 2007, Schafer et al. 2008) unless the patient had been given antimicrobial therapy prior to the revision (Trampuz et al. 2007, Malekzadeh et al. 2010). Thus, if all intraoperative cultures were negative, the revisions were defined as having been done for causes other than infection, unless the patient had received antibiotics prior to the revision. Aspirations of joint fluid are considered to have low to moderate sensitivity and high specificity (Lachiewicz et al. 1996, Malhotra and Morgan 2004, Williams et al. 2004). Thus, a positive aspiration was given considerable weight in determining that a revision had been performed due to infection, whereas a negative aspiration had less of an influence in ruling out infection.
G: The presence of purulence has been regarded as a definite sign of infection (Zimmerli et al. 2004, Parvizi et al. 2011b) but it remains a subjective measurement (Biant et al. 2010, Blumenfeld et al. 2010, Molvik et al. 2010). The presence of purulence was therefore only regarded as a definite sign of infection if supported by other observations (e.g. elevated CRP or positive intraoperative cultures) or if negative intraoperative cultures could be explained by previous use of antibiotics.
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