Introduction: Osteomyelitis remains a major clinical challenge in orthopaedics. It is particularly demanding when the infection is associated with a bacterial biofilm and/or antimicrobial drug resistance. Reliable and cost-effective preclinical models are essential for testing new interventions. Prior published rodent fracture infection models employed rats, which are costly compared to murine models.
Aim: To develop a dependable and cost-effective murine bone infection model with a needle insertion surgery (NIS) that mimics bacterial bone infections associated with biofilm and metal implants.
Methods: A metaphyseal bone infection model with tibial drilled hole (TDH) and needle insertion surgery (NIS) were compared in C57BL/6 mice (female, N=80). Metal pins were inserted selectively into the medullary canal adjacent to the defect sites. A free Staphylococcus aureus (ATCC-12600) or biofilm (ATCC-25923) suspension was locally inoculated (105 CFU in 5 µL). Animals were monitored for physiological or radiographic evidence of infection without prophylactic antibiotics for up to 14 days. At the endpoint, bone swabs, soft-tissue biopsies and metal pins were taken for bacterial culture. X-ray and micro-CT scans were performed along with histology analysis.
Results: TDH and NIS methods achieved a 100% success rate of infection in tibiae when a pin was present with free bacteria injection. NIS is a faster and less complex procedure than TDH, causes less physical disability to the animals. A biofilm inoculation alone induced 40-50% of infections without a metal implant, significantly higher than free bacteria (30%).
Conclusions: To reliably create progressive osteomyelitis, either a metal surface permissive for biofilm formation needs to be present, or defects are inoculated with an established biofilm. The NIS method is a practical approach to produce a bone defect suitable for modelling surgery-related osteomyelitis. Subsequent studies will apply these preclinical models to trial antimicrobial therapies.