Polymicrobial periprosthetic joint infections of the hip and knee : characteristics and management

The aim of this study was to evaluate the clinical and microbiological characteristics, surgical and antibiotic strategies, and long-term outcomes in patients with polymicrobial periprosthetic joint infection (PJI).

This retrospective cohort study was undertaken at a tertiary healthcare centre and included patients aged ≥ 18 years with polymicrobial PJI treated with two-stage or multistage exchange of implants between January 2013 and May 2020. The modified European Bone and Joint Infection Society (EBJIS) criteria were used for the diagnosis of PJI. Surgical and antibiotic treatment followed a standardized institutional algorithm. Outcomes were assessed using Delphi international multidisciplinary consensus criteria and function was classified into categories of mobility. Statistical analyses included Kaplan-Meier survival curves and logistic regression for the identification of risk factors.

A total of 39 patients were included; 24 hip and 15 knee PJIs. Staphylococci (n = 26; 67%), Gram-negative bacilli (n = 15; 38%), and enterococci (n = 14; 36%) were the most frequently isolated pathogens. The median interval between explantation and reimplantation was 91 days, with a median of three revisions required for infection control. Postoperative antibiotic regimens commonly included β-lactams with glycopeptides or lipopeptides, followed by biofilm-active oral antibiotics. The rates of infection-free survival at one, two, and three years were comparable for hip and knee PJIs (76% (95% CI 52 to 89) and 65% (95% CI 31 to 85), respectively; p = 0.121), but there was signicantly better long-term survival after four years for hip PJIs (76% (95% CI 52 to 89) vs 43% (95% CI 9 to 75); p < 0.001). Recurrent infection occurred in ten patients (26%), with difficult-to-treat (DTT) pathogens significantly influencing the failure of treatment. Functional outcomes varied, with 13 patients (33%) regaining independent mobilization.

Polymicrobial PJI remains a difficult condition to treat, with high morbidity requiring a tailored multidisciplinary approach. While standardized surgical and antibiotic strategies improve infection control, DTT organisms, and previous revision procedures increase the risk of recurrent infection. The poor long-term functional outcomes highlight the need for further optimization of treatment protocols to enhance patients' mobility and quality of life.