Unexpected Positive Cultures in Hip and Knee Periprosthetic Fractures

The purpose of this study was to determine the prevalence of unexpected positive cultures noted at the time of revision surgery for periprosthetic fracture 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.This was a single center retrospective review of 270 patients undergoing surgery for periprosthetic fractures from December 2010 to December 2021. Exclusion criteria included: open fractures; history of infection at fractured joint; non-operatively treated patients; and intra-operative fractures. The primary endpoint was the prevalence of unexpected positive cultures noted at the time of revision surgery. This was defined as one or more positive culture in a periprosthetic fracture 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.During the study period, 159 patients were admitted with periprosthetic fractures of the hip and 61 with periprosthetic fractures of the knee. 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, six 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 non-infected patients showed a significant association between preoperative C-reactive Protein (CRP) > 10 mg/ml (P=0.04), loose implant (P=0.07), and infection.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.