Experimental models in orthopedic infection research

Osteomyelitis is a devastating disease of the bone tissue and is a severe complication in orthopedic and trauma surgery, especially when combined with prostheses and osteosynthesis. The infection risk of a prosthesis/osteosynthesis is depending on the location of the implant and the health status of the patient. Hip and knee prostheses have an infection risk of up to 4%, while osteosynthesis has a considerable higher infection risk of up to 30%. Considering the increasing number of implants being placed every year and a stable infection rate of these implants, this will result in an increasing prevalence of implant infections. Infection treatment, however, is based on local antibiotic treatment often combined with surgical debridement. In general, a two-stage revision is suggested to be the most effective infection treatment with success rates of up to 93%. Infection prevention, on the other hand, is based on the prevention or delay of bacterial adhesion on the implant surface and to provide a more suitable surface for eukaryotic cells to survive and adhere to it. To study implant infection and to assess novel implant strategies and coatings, experimental animal models are essential. The earliest models date from 1883, which were rather simple in setup. During the last decades, these models became more complex and required less animals. This chapter provides both an overview of experimental models as well as scoring systems to quantify orthopedic infections (ranging from hematological, radiological to histological perspectives). Still there is no ideal model to assess every orthopedic infection; it will always require a dedicated model depending on the research question.