The Journal of Bone and Joint Surgery, Vol 70, Issue 10 1551-1557, Copyright © 1988 by Journal of Bone and Joint Surgery, Inc
Release of gentamicin from acrylic bone cement. Elution and diffusion studies
AS Baker and LW Greenham
Department of Microbiology, University of Bristol, England.
It has been generally assumed that release of antibiotic from
methylmethacrylate occurs either from the surface, through pores in the
matrix of the cement, or by diffusion through the matrix. In vitro and in
vivo studies of the release of antibiotic from cement have produced
variable and inconsistent results. In our laboratory, preliminary
observations suggested that antibiotic is released from methylmethacrylate
by flow through an interconnecting series of voids and cracks in the
cement, rather than through diffusion after having been homogeneously
distributed throughout the cement. Therefore, experiments were performed to
answer the fundamental question of whether the matrix of methylmethacrylate
bone cement is permeable to gentamicin. In vivo elution studies were
performed on injection-molded rods of methylmethacrylate that had been
loaded with two different amounts of gentamicin. The first group of rods
contained 0.5 gram of gentamicin for each packet and the second, 1.5 grams
for each packet. The rods were embedded subcutaneously in the subcostal
region of sheep for three months. Bioassay of sections of the rods, using
the tube-diffusion technique of Mitchison and Spicer, showed that the more
highly loaded cement had released a significantly greater proportion of
gentamicin. This occurred because the more highly loaded cement contained a
greater number of defects that contained gentamicin (filled voids and
interconnecting cracks). In vitro diffusion studies were also performed,
using 0.8-millimeter-thick disks of methylmethacrylate that did not contain
antibiotic. Test solutions of either gentamicin or methylene blue were
placed in the inner compartments of diffusion chambers. The outer
compartments contained tissue-culture medium 199, which was sampled monthly
and assayed for gentamicin or methylene blue.(ABSTRACT TRUNCATED AT 250
WORDS)
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