GENTAMICIN LEVELS IN DIAGNOSTIC ASPIRATES FROM PATIENTS WITH HIP AND KNEE ARTROPLASTY

Joint fluids obtained for diagnostic purposes from 25 patients were assayed for the presence of gentamicin. All of the patients had presented with failing or painful joints at periods up to 10 years following primary hip or knee arthroplasty using gentamicin-impregnated cement. Gentamicin was detected in the joint fluids from 9 of 15 patients with knee prostheses and 4 of 10 with hip prostheses. Gentamicin concentrations ranged from 0.06mg/L to 0.85 mg/L with no significant differences in concentration between patients with hip or knee prostheses, or type of prosthesis, and no identifiable relationship was found gentamicin concentration and the time after primary arthroplasty. Although the majority of the gentamicin concentrations were found to be below the levels required to inhibit susceptible pathogens, we conclude that gentamicin release around failing implants may lead to false negative cultures in some patients and provide selective pressure for the emergence of resistance where infection is present in others.