Abstract
Introduction: In-vivo elution studies on Antibiotic-loaded Bone Cement (ABC) have concentrated on the short to medium term. This unit has previously described gentamicin release from cement during revision surgery and its presence in the joint aspirates of THAs at up to 12 years. We elected to study the late elutional behaviour of gentamicin-loaded cement in THA.
Methods: 51 patients undergoing revision THA surgery, for aseptic failure, at our centre were studied. Details of the original operation and the subsequent clinical and radiographic course were noted. Pre-operative urine samples and intra-operative joint fluid aspirates (prior to cement disruption) were assayed for their gentamicin concentrations using a fluorescence polarisation immunoassay (Abbott TDX). Cement samples underwent a Bacillus subtilis agar plate inhibition bioassay to assess for antimicrobial activity.
Results: Urine samples were obtained in 43 (84%) of the cases. All were negative for gentamicin (sensitivity level of 0.06 mg/L). Cement samples were retrieved in 36 cases (71%) and all of these (100%) demonstrated significant antimicrobial activity when compared to a standard 10 mg gentamicin disc. In 25 cases (49%) the joints were aspirated and 8 (32%) of these had a gentamicin concentration > 0.1 mg/L. The concentrations however were all below the Minimum Inhibitory Concentration (MIC) for intermediate sensitivity organisms. The longest interval between the primary and revision operations, in these positive cases was 25 years!
Conclusions: This study uniquely demonstrates sequestration of gentamicin within cement for up to 27 years. In addition, one third of joint aspirates had detectable though subtherapeutic gentamicin concentrations at up to 25 years. There was no evidence of late systemic release. These low concentrations of antibiotics, released after many years, are probably a potent stimulus to the emergence of resistant organisms. The use of antibiotic-loaded bone cement in primary THA remains controversial and requires further scrutiny.
The abstracts were prepared by Mr Peter Kay, Editorial Secretary. Correspondence should be addressed to British Hip Society, The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
