SYNOVIAL FLUID ANTIBIOTIC LEVELS AT STAGE II REIMPLANTATION FOLLOWING EXCHANGE ARTHROPLASTY

Abstract

Purpose: The gold standard for treatment of infected total hip or knee replacements remains a 2-stage exchange arthroplasty. This includes aggressive irrigation and debridement, implant removal, insertion of antibiotic impregnated spacers, iv antibiotics, and eventual reimplantion with a definitive prosthesis. The purpose of this study was to quantify Vancomycin and Gentamycin synovial fluid levels at the time of reimplantation following a 2-stage exchange arthroplasty for a infected total hip or knee replacements.

Methods: The senior author performed 42 two-stage reconstructions using the prosthesis of antibiotic-loaded acrylic cement (PROSTALAC). Each 40g bag of Pala-cos-R cement was impregnated with Vancomycin 2g, Gentamycin 4.8g, and plus/minus ancef 2.0g (depending on penicillin allergy). At the time of reimplantation, the synovial fluid was immediately analyzed for levels of Vancomycin and Gentamycin.

Results: 17 patients were taken for stage II within 60 days (avg. 53). The synovial fluid vancomycin and gentamycin levels were 12.7 and 20.6 respectively. Twelve patients had stage II between 60 and 90 days (avg. 79). The synovial fluid vancomycin and gentamycin levels were 6.2 and 14.9 respectively. The remaining 13 patients underwent stage II beyond 90 days (avg. 192), and their synovial fluid vancomycin and gentamycin levels were 3.3 and 2.4 respectively. 40 of 42 patients had their infections eradicated.

Conclusions: in vitro evidence predicts that antibiotics elute rapidly from bone cement. The results of this study confirm that substantial doses of vancomycin, gentamycin, and ancef per bag of Palacos-R cement does confer long term synovial fluid antibiotic levels well above the minimal inhibitory concentrations required to treat infected total joints. When stage II reimplantation is done at greater than 3 months, synovial fluid antibiotic levels decline significantly.