Many orthopaedists order cultures of tissue and synovial fluid samples during the reimplantation phase of two-stage exchange arthroplasties. Now, thanks to a retrospective study by Tan et al. in the August 3, 2016 JBJS, surgeons have some guidance on how to interpret the results from such cultures.The authors reviewed 267 cases of periprosthetic joint infections (186 knees and 81 hips) that were treated with two-stage exchange arthroplasty. Intraoperative tissue samples were obtained at the time of reimplantation, and 33 joints (12.4%) were found to have one or more positive cultures. Of those 33 cases, 15 (45.5%) had a subsequent arthroplasty failure, compared with 49 (20.9%) of the cases that were culture-negative at reimplantation. Failure rates did not differ between cases with 1 positive culture and those with ≥ 2 positive cultures.
After controlling for other variables, the authors determined that a positive intraoperative culture at the time of reimplantation was independently associated with >2.5 times the risk of subsequent treatment failure. These findings prompted Tan et al. to conclude that “even single positive cultures…should be treated aggressively.” They report that at their institution (the Rothman Institute in Philadelphia), “any positive culture at the time of reimplantation is now considered important…and is treated with systemic antibiotics.”
Among the limitations of this study is its inability to accurately assess the impact of antibiotic treatment in patients with positive cultures. The authors also stress the need for further evaluation of rapid intraoperative diagnostic tools that have shown promise in determining infection eradication more quickly than cultures can.