Bone reaction to the implant of intramedullary pins of three different metals in rat femur

Abstract

A bone-implant interface is influenced by several factors, such as chemical composition of the implanted material, stress transfer at the interface and the biology of the living model. Histological and vascular tree injection methods were used to assess the response to intramedullary pins, cast in different metallic alloys and implanted in the medullary canal of rat femora. A remarkable endosteal reaction, with an absence of major damage of the medullary vascular supply, was observed. Remodelling of this woven bone led to the formation of a lamellar bony shell around the pins, while in sham operations (pin inserted and soon removed) the former was completely resorbed in about 20 days. Mechanical trauma seems to be sufficient to evoke the response of the endosteum, which does not differ from that observed in the normal repair process of diaphyseal fractures. Bone grew very close to the metal surface, but a thin connective membrane or a layer of amorphous material was present at the interface with stainless steel, Co-Cr and titanium pins. Histology of the interface suggests that the implants were not mechanically neutral; these observations may be correlated to the thin layer of bone observed around hip cementless prosthetic stems in patients.