A: A PJI was defined by microbiology if the same microorganism was isolated from 3 or more biopsies taken during surgery (Kamme and Lindberg 1981, Atkins et al. 1998)
B: Revision THA was classified as being due to causes other than infection if: ≥ 5 intraoperative cultures were taken and all of them were negative (Atkins et al. 1998, Trampuz et al. 2007), the patient was not treated with antibiotics prior to revision (Trampuz et al. 2007, Malekzadeh et al. 2010), and there was no positive culture from the aspiration of joint fluid (Lachiewicz et al. 1996, Malhotra and Morgan 2004, Williams et al. 2004).
C: If any of the statements in B were positive, the medical record was reviewed to identify whether a sinus tract communicating with the prosthesis had been observed (Zimmerli et al. 2004, Parvizi and Gehrke 2013).
D: If more than 5 intraoperative cultures had been taken, an audit was performed by the authors in order to classify the revision as having been performed due to PJI or no infection. The audit was done to ensure that 2 or more positive cultures did not automatically lead to a revision being classified as deep infection if the 2 positive cultures were the result of a large number of intraoperative cultures (e.g. 10–15).
E: If the CRP was >10 mg/L and had been measured within 30 days before the date of revision, the indication for performing the revision was classified according to the algorithm (continued in Figure 3) using the result of aspiration, intraoperative cultures (with prior use of antibiotics taken into account), and the presence of purulence. If CRP was not measured or it was <10 mg/L, the revision was classified as being due to other causes (Bernard et al. 2004, Savarino et al. 2004, Schinsky et al. 2008).
Note: For all stages in Figure 3, it is an underlying premise that the CRP was measured and found to be >10 mg/L.