Development of a hematogenous implant-related infection in a rat model Orthopedics and biomechanics

Background: Implant-related osteomyelitis is a major complication that requires immediate treatment, often involving removal of the implant, prolonging patient recovery and inflating expenses. Current research involving interventions to diminish the prevalence of such measures include investigating prophylactic and therapeutic remedies. A proper and accurate animal model is needed to thoroughly investigate such treatments. The scope of this project was to develop an animal model in which a consistent and measurable infection can be formed on an orthopedic implant when bacteria is introduced via a hematogenous source. Methods: Titanium Kirschner-wires were implanted into the intramedullary canals of both femurs. Staphylococcus aureus, ranging from10⁴ to 10⁹ colony forming units, was injected into a tail vessel. After a designated time (3, 7, 14, or 42 days) the femurs were harvested and bacterial numbers determined for both the femur and the implanted K-wire. In addition, histology and micro-computed tomography were used as subjective tools to further characterize the infection. Results: Consistent infection, that is infection of ≥75 % of the femurs, wasn't achieved until 10⁷ CFU∈S. aureus was injected. At 10⁷ CFU, the femurs contained 4.6x10⁶ CFU/g bone tissue at day 3 and 4.8×10⁸ CFU/g bone tissue by day 14. The wire showed comparable contamination with 4.8×10⁴ CFU/mm² at day 3 and 3.7×10⁵/mm² by day 14. After 42 days, the bacteria number decreased but was still occupying at 1.9×10⁵ CFU/g bone tissue. There were morphological changes to the bone as well. At day 42, there were signs of osteonecrosis and active bone formation when compared to control animals that received a K-wire but were inoculated with saline. Conclusions: A model for hematogenous osteomyelitis, a common complication associated with implants, has been introduced. A reproducible, preclinical model is essential to evaluate future methods used to mitigate blood-borne bacteria hardware and bone infections.