Presumed aseptic orthopaedic implant revisions: unmasking hidden infections and shaping future directions

Unexpected positive cultures (UPCs) during revision of orthopaedic implants in presumed aseptic revision surgeries represent a significant clinical challenge; indeed, it is very difficult to state whether a positive culture indicates a true infection or merely sample contamination. In hip, knee, shoulder, elbow and spinal procedures, the incidence of UPCs remains clinically relevant, ranging from approximately 7% in elbow revisions to approximately 28% in spinal revisions. The organisms most commonly isolated - coagulase-negative staphylococci (23-52%) and Cutibacterium acnes (24-65%) - are classic low-virulence pathogens with high contamination potential, reinforcing the uncertainty that accompanies their detection. Although published outcomes vary, most studies suggest that a single UPC rarely compromises implant survivorship, supporting the interpretation that many isolated findings represent contamination rather than infection. In contrast, multiple cultures positive for the same organism indicate occult infection more strongly, as highlighted by the International Consensus Meeting 2023 guidelines, which associate concordant multi-culture positivity with a higher risk of re-revision or failure. Consequently, the emerging clinical consensus is that single low-virulence UPCs can often be observed, whereas multiple concordant UPCs warrant management as true infection, guiding decisions regarding antimicrobial therapy and postoperative surveillance. Given the persistent variability in published management strategies, further study is needed to standardize responses to UPCs. Finally, rapid, cost-effective intra-operative diagnostics may ultimately improve real-time detection of infection, and reduce uncertainty in revision of orthopaedic implants.