S02.3 SONICATION OF TEMPORARY DEVICES (SPACERS AND CEMENT NAILS) INSERTED DURING A TWO-STAGE IMPLANT EXCHANGE IN PATIENTS WITH PROSTHETIC JOINT INFECTION

Abstract

Background: Antibiotic-loaded spacers and cement nails are commonly used in patients undergoing a two-stage implant exchange procedure for treatment of prosthetic joint infection (PJI). During re-implantation 2–6 weeks after implant removal, tissue specimens are collected to document successful eradication of infection. However, these specimens have limited sensitivity, especially in patients receiving antimicrobial treatment. We investigated the value of sonication of removed spacers and cement nails.

Methods: We prospectively included patients in whom a spacer or cement nail was removed from January 2007 through April 2009 during a two-stage exchange procedure. The removed temporary device was sonicated in a container with Ringer’s solution in an ultrasound bath for 5 min at 40 kHz (as described in NEJM2007;357:654). The resulting sonication fluid was cultured aerobically and anaerobically for 10 days. In parallel, > 2 tissue samples were collected for conventional cultures on blood agar plates and enrichment broth. PJI was defined as visible purulence, acute inflammation on histopathology, sinus tract or significant microbial growth in tissue or implant sonication cultures.

Results: In this ongoing study, 28 spacers and 10 cement nails from patients with confirmed PJI were included (median age 75 y; range 49–86 y). All devices were impregnated with antibiotics (gentamicin and/or vancomycin) and were placed in the hip (n=21), knee (n=9) or shoulder joint region (n=7). At the time of explantation, the following pathogens were isolated: coagulase-negative staphylococci (n=19), Staphylococcus aureus (n=7), Streptococcus agalactiae (n=3), Propionibacterium acnes (n=5) and mixed infection (n=4). All patients received systemic antibiotics for a median of 19 days (range 11–42 days) before removal of the spacer/nail. At the time of re-implantation, tissue cultures were negative in all 38 patients, whereas sonication cultures showed growth of Propionibacterium acnes in 2 of 38 patients (5%) with a hip and shoulder spacer, both in significant numbers (150 and 550 colonies/ml sonication fluid, respectively). These organisms were probably present as mixed infection already at the time of explantation, but were missed due to overgrowth due to another organism (S. aureus in one patient and coagulase-negative staphylococci in another). Both patients were not initially treated for the Propionibacterium acnes infection, but the treatment was given after re-implantation.

Conclusion: Sonication of removed spacers is a suitable approach to identify persistent infection in patients with a two-stage exchange. Sonication may replace the current standard approach consisting of multiple tissue specimens in order to document successful eradication of infection.