Relation of surface area to in vitro elution characteristics of vancomycin-impregnated polymethylmethacrylate spacers

To study the relationship between surface area and antibiotic elution from antibiotic-impregnated polymethylmethacrylate (PMMA) spacers, a standard block spacer made of vancomycin (4 g) and 40 g of PMMA was compared with two unique spacer designs, the "donut" and "fenestrated." The spacers were incubated in phosphate-buffered saline, which was changed daily, and a microbiologic assay was used to measure the antibiotic activity of the eluates. The donut and fenestrated spacers had 12% and 40% more surface area than the standard spacer, respectively. There was no significant difference, however, in daily elution levels of antibiotic between the donut spacer and the standard spacer. The fenestrated spacer displayed significantly better elution than either the standard or donut spacers, with an average of 20% more antibiotic eluted on any given day.