A study by Miller et al. in the February 20, 2019 issue of JBJS provides preclinical proof of concept that antibiotic-loaded coatings on orthopaedic implants could eventually reduce the incidence of implant-associated infection.
The researchers used in vivo bioluminescence imaging (BLI) and ex vivo analysis of colony-forming units (CFUs) to show the efficacy of an implant coating that released linezolid-rifampin over a 7-day period. Through a parapatellar arthrotomy, researchers reamed the femoral canal of 12 rabbits and inoculated the canals with a bioluminescent strain of MRSA. They then inserted a surgical grade titanium peg into each canal. All of the pegs were coated with a nanofiber coating; 6 of the pegs were loaded with the antibiotic coating and 6 were not.
Implants coated without antibiotics were associated with significantly increased in vivo BLI signals and significantly increased knee width, relative to implants with the antibiotic-releasing coatings. The animals were killed on day 7, and ex vivo analysis of CFUs isolated from soft tissue, bone, and implant specimens showed significantly increased CFUs in the specimens without the antibiotic-releasing coating, while CFUs were undetectable in the implants with antibiotics.
This larger-animal model to assess bacterial burden employed a clinically used orthopaedic implant and replicated a medial parapatellar arthrotomy in humans. According to the authors, the coating used is “highly versatile, and the polymers or drug concentrations could be modified for more rapid or longer release.” This rabbit model should be amenable to studying additional antibiotic-releasing strategies for possible translation to clinical research in humans.