Evaluation of Antibiotic-Impregnated Microspheres for the Prevention of Implant-Associated Orthopaedic Infections

Background: Prevention of infection associated with uncemented orthopaedic implants could lead to improved implant stability and better patient outcomes. We hypothesized that coating porous metal implants with antibiotic-containing microspheres would prevent infections in grossly contaminated wounds. Methods: Bioresorbable polymer microspheres containing tobramycin were manufactured and pressed into porous metal cylinders that were then implanted into radial defects in rabbits. Control implants that did not contain antibiotic microspheres were also implanted into the contralateral limbs. Each implant was then contaminated with Staphylococcus aureus prior to closure of the wound. The animal was euthanized after clinical signs of infection appeared, or at two weeks after surgery. Periprosthetic tissue was cultured for the presence of S. aureus, and integration of the implant with the surrounding bone was measured. Results: The antibiotic microspheres successfully prevented infection in 100% of the eleven limbs with treated implants, which represented a significant improvement (p = 0.004) compared with the infection rate of 64% (seven of eleven) for the limbs with control implants. Implant integration averaged 38.87% +/- 12.69% in the fifteen uninfected limbs, which was significantly better (p = 0.012) than the average of 19.46% +/- 14.49% in the seven infected limbs. Conclusions: The antibiotic delivery system successfully prevented infection in 100% of the cases studied, resulting in an increase in implant integration.