When More Is Worse: Multiple Cultures Predict PJI Treatment Failure

Commentary The management of periprosthetic joint infection (PJI) remains one of the most challenging and devastating problems in knee arthroplasty surgery. As noted in this article by Tarabichi et al., the per annum cost of PJI in the U.S. is approaching $2 billion and concomitantly reduces patient, financial, physician, and health-care system resources1,2. While 2-stage exchange arthroplasty has been the gold standard treatment in North America for decades, failure rates remain as high as 30% or more3–5. Traditionally, treatment prognosis has been tied to patient comorbidities, the duration of PJI, and the virulence of the organism. Tarabichi et al. provide important new evidence about prognostic factors that may help surgeons better predict outcomes and potentially modify treatment approaches. This well-designed multicenter study of 299 patients who had undergone 2-stage exchange for the treatment of chronic knee PJI demonstrated that patients with ≥2 positive cultures at the time of resection had an eightfold higher risk of failure compared with those with a single positive culture. The authors carefully controlled for potential confounding variables, including organism virulence, prior failed PJI treatment, and demographic characteristics. The finding that 95.8% of treatment failures occurred in patients with multiple positive cultures, compared with only 75.3% of treatment successes, is particularly striking and raises the potential for organism burden as another prognostic variable in treatment. Although the study’s limitations include its retrospective methodology and inability to fully standardize preoperative antibiotic administration and culture site specimen collection, the conclusions are still likely robust. Several aspects of this study deserve emphasis. First, this represents the first investigation to specifically examine the relationship between culture number and outcomes in PJI treatment. While previous work has suggested that bacterial burden correlates with outcomes in other settings such as bacteremia, this had not been demonstrated in PJI. Second, the large sample size and multicenter design strengthen the validity of the findings. Third, the authors’ careful methodology, including standardized culture techniques and clear outcome definitions, provides greater confidence in the results. The clinical implications are noteworthy. The presence of multiple positive cultures at resection may identify patients who would benefit from more-aggressive treatment approaches, such as extended antibiotic therapy, both after resection and after reimplantation, as well as additional irrigation and debridement procedures before reimplantation. Importantly, this finding could help to counsel patients about their prognosis, timeline expectations, and mental health concerns, and it potentially could influence the timing of reimplantation in selected cases. Another important aspect of this study was the utilization of an already existent, commonly utilized, and relative low-cost methodology as a predictor of treatment failure. I commend the authors on a compelling study addressing an important topic, and future research should focus on whether modifying treatment protocols on the basis of culture number can improve outcomes. For now, surgeons should consider culture number as an important prognostic factor when treating PJI and potentially adjust their treatment approach accordingly in patients with multiple positive cultures.