The infected orthopaedic implant. An animal model to study the mechanisms of haematogenous infection of cementless implant materials

There is a lack in basic and clinical knowledge on the pathogenesis of orthopaedic implant infections, particularly as a sequel of a bacteremia. In the present study an experimental animal model was developed, that allows us to study haematogenous infections of cementless implants. Ten New Zealand White rabbits were subjected to a two-stage surgical procedure. A cylindrical Ti6Al4V or hydroxyapatite coated Ti6Al4V implant was inserted into the right tibia. After a period of at least 4 weeks, the implants were selectively contaminated with varying doses of Staphylococcus aureus, via the right femoral artery. During the postoperative period, the animals were examined daily and blood samples were taken. After at least 1 week, the animals were sacrificed and biopsies of bone, marrow, liver, spleen, lung and kidney were cultured. The remaining implant with surrounding bone was prepared for histological examination. Injection of 5 × 10⁸ cfu causes positive cultures in all cases and minimal systemic reactions. On the histological sections, incidental bacteria and signs of a mild, focal inflammation were seen. This animal model is useful for further studies of interface, treatment and prevention aspects of haematogenous implant infections.