Unexpected Positive Cultures in Hip and Knee Periprosthetic Fractures.

BACKGROUND:The purpose of this study was to determine the prevalence of unexpected positive cultures noted at the time of revision surgery for periprosthetic fracture (PPF) after total hip or knee arthroplasty. Moreover, we evaluated whether this finding should be considered clinically significant and what type of treatment, if any, was required. METHODS:This was a single-center retrospective review of 270 patients undergoing surgery for PPFs from December 2010 to December 2021. Exclusion criteria included: open fractures; history of infection at fractured joint; non-operatively treated patients; and intraoperative fractures. The primary end point was the prevalence of unexpected positive cultures noted at the time of revision surgery. This was defined as one or more positive cultures in a PPF that the surgeon had preoperatively classified as aseptic according to the 2018 International Consensus Meeting. Data collection included patient demographics, medical histories, preoperative investigations, postoperative microbiology, and treatment. RESULTS:During the study period, 159 patients were admitted with PPFs of the hip and 61 with PPFs of the knee. The mean age was 70 years (range, 32 to 93 years). Unexpected positive cultures were diagnosed postoperatively in 15 patients (6.8%; 10 hips, 5 knees). The most prevalent organism was Staphylococcus epidermidis (35.0%). Of those 15 patients, 6 required a surgical revision for infection. None of the patient-related risk factors were found to be associated with an increased risk of unexpected positive cultures. The comparison between infected and noninfected patients showed a significant association between preoperative C-reactive protein >10 mg/mL (P = .04), loose implant (P = .07), and infection. CONCLUSIONS:The prevalence of unexpected positive cultures was 6.8% in our study cohort. Although surgical treatment may be required, the majority of patients seem to require no treatment. Larger series are required to investigate the clinical importance of this rare finding. LEVEL OF EVIDENCE:III.