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Objective: To test the hypothesis that antibiotic-laden polymethylmethacrylate (PMMA) pin sleeves prevent infection around skeletal external fixation pins., Design: An experimental study using an animal model was conducted., Animals: In each of five goats, three four-millimeter half-pins were placed in the left and right iliac crests, for a total of thirty half-pins. The pins were infected with one milliliter of broth containing 7.6 x 10(5) colony-forming units per milliliter of Staphylococcus aureus (ATCC 25923)., Intervention: The pins in the right iliac crest were treated with the tobramycin-impregnated pin sleeves, and the pins in the left iliac crest (control) were left untreated., Results: The results showed clinical evidence of infection (i.e., looseness and gross pus) and heavy bacterial growth (average 6.8 x 10(10) colony-forming units per milliliter) for the untreated pins, but no clinical evidence of infection and no bacterial growth at forty-eight hours for the treated pins., Conclusion: The present results indicate that the use of the antibiotic-impregnated PMMA pin sleeve can prevent the development of pin-tract infection and appears to prevent colonization of the external fixation pins.

Aminoglycoside-impregnated polymethylmethacrylate beads, which are used to deliver antibiotic directly to infected sites in the musculoskeletal system, are available as a manufactured product or they can be mold-made by a pharmacy or hand-rolled by the orthopaedist in the operating suite. We investigated the leaching of antibiotic from each of these types of beads. Our hypothesis was that the elutions of antibiotic from the three types of beads are similar. Three study groups (hand-made, mold-made, and manufactured beads), each composed of four five-bead subsets, were formed so that twenty beads of each type were tested. Each bead was leached daily in a two-milliliter aliquot of normal saline solution throughout a sixty-day period, and the aminoglycoside concentration in twenty of these aliquots was determined. Analysis of variance showed no statistically significant differences when the antibiotic elutions within each subset, between the different subsets, and between the three groups were compared. The clinically important finding of this investigation is that the leaching characteristics of the three types of aminoglycoside-impregnated beads are equivalent when the beads have been fabricated out of comparable materials.

The effect of antibiotic bead chains on the evolution of infection cannot be studied entirely in man due to the ethical problems of obtaining valid controls. Therefore, a model of musculoskeletal injury was devised in rabbits by making a paraspinal wound, fracturing a spinous process, and contaminating the wound with 1 x 10(4) colony-forming units/ml of Staphylococcus aureus. These contaminated wounds were treated with tobramycin-containing polymethylmethacrylate (PMMA) beads. Control rabbits were either treated with PMMA beads that did not contain antibiotic, treated with IM tobramycin, or left untreated. At 5 days, six of eight animals treated with antibiotic-impregnated beads had no recoverable organisms. Six of eight rabbits receiving IM tobramycin had wound infections, and five of five in whom non-antibiotic-containing beads had been implanted had significant wound infections, with one of the five dying of sepsis on the 3rd day of the experiment. The clinical course of infected controls was the same as the course of those animals receiving IM antibiotics and the same as those in whom beads without antibiotics were implanted. That is, the rabbits had grossly infected wounds and the organisms recovered were of the same type as those implanted. This research shows a highly statistically significant effect of tobramycin-containing antibiotic beads in retarding the evolution of an experimental Staphylococcus infection in rabbits.