Risk Factors and Outcome

Limited data are available regarding the risk factors and outcome of polymicrobial prosthetic joint infection (PJIs) when compared with monomicrobial PJI. Between January 1998 and November 2006, we ret- rospectively identified 34 of 174 prosthetic joint infections (19%) were polymicrobial. The 2-year cumulative proba- bility of success of treating polymicrobial and mono- microbial PJIs was 63.8% and 72.8%, respectively. Twenty-six percent, 38%, and 29% of PJIs were treated with two-stage exchange, debridement and retention, or resection arthroplasty, respectively, and the 2-year survival rate free of treatment failure in each group was 77.7% (95% confidence interval, 42.8%-94.2%), 52.7% (95% confidence interval, 28.4%-75.9%), and 64.2% (95% confidence interval, 28.7%-88.9%). Methicillin-resistant Staphylococcus aureus (26.4% versus 7.1%) and anaerobes (11.7% versus 2.8%) were more common in polymicrobial PJIs. Polymicrobial PJIs occurred in patients with a soft tissue defect/dehiscence (23.5% versus 2.8%), drainage (79.4% versus 39.2%), or prior local irradiation (8.8% versus 0.71%). We found the following factors associated with polymicrobial prosthetic joint infections: the presence of a soft tissue defect/wound dehiscence (odds ratio, 5.9), drainage (odds ratio, 5.0), and age 65 years or older (odds ratio, 2.8). Level of Evidence: Level III, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.