Periprosthetic joint infection by Propionibacterium acnes: Clinical differences between monomicrobial versus polymicrobial infection.

Objective: To compare a series of monomicrobial Propionibacterium acnes (P. acnes) knee and hip periprosthetic joint infection (PJI) cases with cases of polymicrobial PJI which included P. acnes. We hypothesized that the presence of a polymicrobial P. acnes infection would lead to worse outcomes than those in cases of monomicrobial P. acnes PJI.

Methods: Retrospective multicentre study. All patients with hip or knee PJIs including P. acnes diagnosed from August-2002 to July-2013 in two university hospitals were included. We collected demographic data, McPherson classification, local signs of infection (swelling or wound drainage), laboratory and histological data, surgical management, antibiotic treatment and outcomes. Data were compared between two groups: cases of monomicrobial P. acnes PJI, and cases of polymicrobial PJI involving P. acnes.

Results: Thirty-eight patients who presented with 38 PJIs were included; median age was 71 (IQR:62.5-79); 21 were men (55%); median follow-up was 42 months (IQR:17.5-58). Local signs of infection were present in 14 patients (36.8%); ESR>30 mm/h in 14 patients (36.8%); CRP>1 mg/dl in 15 patients (39.5%); 11 out of 25 patients (44%) had positive preoperative cultures from joint aspiration. Positive histologic studies (Feldman's criteria) were found in 5 out of 28 patients (17.8%). Twenty-four patients (63%) had monomicrobial PJIs; 14 patients (37%) had polymicrobial PJIs. There were no significant outcome differences between monomicrobial and polymicrobial PJIs cases; overall, the success rates were 79.2% and 85.7% respectively (P > 0.05).

Conclusions: We did not find any significant differences between monomicrobial and polymicrobial P. acnes PJI outcomes. ESR, CRP and histologic study are established parameters for diagnosing PJI which did not prove useful in P. acnes PJI.