Undiagnosed Periprosthetic Infections in First-Time Aseptic Revision Hip Arthroplasties

<b>Background</b>: Unexpected infections diagnosed after intraoperative cultures in aseptic revision hip arthroplasties are infrequent, but the features and outcomes of culture-positive cases are still poorly understood. A single-center retrospective study was conducted to assess the following: (1) the incidence, (2) the profile of the cases, and (3) the outcomes of the revision hips performed for presumed aseptic reasons that became septic after intraoperative cultures. <b>Methods:</b> Instances of first-time aseptic revision hips (a retrospective cohort study) in the hospital database were reviewed. The revisions with the isolation of two phenotypically identical microorganisms in the intraoperative cultures were selected. The profile (bacteria, pre-operative markers) and the outcomes of the revisions (survival rates, complications, reasons for re-revision) were assessed. <b>Results:</b> Out of 424 cases of presumed aseptic revision hip arthroplasty, 19 patients (4.48%) were classified as septic. <i>Staphylococcus epidermidis</i> (9, 47.37%) was the most frequent microorganism. In three patients (15.8%), C-reactive protein and erythrocyte sedimentation rate values were higher, and in only one case (5.26%), C-reactive protein values and the white blood cell count were elevated. An antibiotic therapy was administered in every case. At a mean follow-up of 3.72 ± 2.18 years, three patients (15.79%) experienced complications (dislocation, pain without loosening, chronic suppressive antibiotic therapy) and two patients (10.53%) required re-revision for septic relapse (same microorganisms). The survival rate of the cohort was 89.47% (95% CI: 64.08-97.26) at 2 and 4 years. <b>Conclusions:</b> Missed periprosthetic infections rarely occurred in presumed aseptic revision hips. However, the outcomes are fair, and septic relapses are not uncommon.