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: (10^2), (10^3), and > (10^4) CFU/rat. We measured clinical signs, inflammatory markers, radiographic signs, histopathology, and bacteriology in the infected animals. Results: An inoculum of at least (10^4) cfu of either wild-type bacterial strain resulted in histological, bacteriological, and radiographic signs of osteomyelitis with loosening of the prosthesis. An inoculum of (10^3) CFU gave signs of osteomyelitis but the prosthesis remained in situ. Bacterial inocula of (10^2) 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 (10^3) CFU/rat, bacteria unable to produce PNAG (ica::tet) had only minor defects in their virulence.