A novel knee prosthesis model of implant-related osteo- myelitis in rats

Abstract

Background and purpose There have been numerous reports of animal models of osteomyelitis. Very few of these have been prosthesis models that imitate human conditions. We have developed a new rat model of implant-related osteomyelitis that mimics human osteomyelitis, to investigate the pathology of infection after orthop edic implant surgery.Methods 2 wild-type strains of Staphylococcus aureus, MN8 and UAMS-1, and their corresponding mutants that are unable to produce poly-N-acetyl glucosamine (PNAG) (ica::tet) were injected into the medullary canals of the femur and tibia at 3 different doses: 102, 103, and > 104 CFU/rat. We measured clinical signs, inflammatory markers, radiographic signs, histopathology, and bacteriology in the infected animals.Results An inoculum of at least 104 cfu of either wild-type bacterial strain resulted in histological, bacteriological, and radiographic signs of osteomyelitis with loosening of the prosthesis. An inoculum of 103 CFU gave signs of osteomyelitis but the prosthesis remained in situ. Bacterial inocula of 102 cfu gave no signs of osteolysis.Interpretation We have established a new knee prosthesis model that is suitable for reliable induction of experimental implant-associated osteomyelitis with the prosthesis in situ, using a small inoculum of S. aureus. At a dose of 103 CFU/rat, bacteria unable to produce PNAG (ica::tet) had only minor defects in their virulence.