This study investigated the effects of wear particles, produced from a number of implant materials, at the bone-implant interface using a small animal model.

Particles were prepared from metal, ceramic and polymer replacement joint components or implant grade stock by grinding the materials against a diamond embedded grinding pad. The mean diameter of the particles ranged from 1.5mm to 3.2mm. Sterilised particles were suspended in sterile saline containing 2% v/v male Sprague-Dawley serum at a concentration of 109 particles per ml.

Seventy-two male Sprague-Dawley rats were assigned to twelve groups of six animals. A ceramic pin was inserted into the right tibia of each animal. Six groups were assigned a particle type with one group acting as vehicle control. 100ml of particle suspension or vehicle was injected into each knee joint at 8, 10 and 12 weeks following implantation and the animals were killed 2 weeks later. Of the remaining five groups, four were assigned a particle type and one was the vehicle control. These animals were injected with 100ml of particle suspension or vehicle at 20, 22 and 24 weeks following pin implantation and were killed 2 weeks later. The tibia and femora were removed, disarticulated and processed for histology. The total gap between pin and bone, including fibrous tissue, was measured.

Specimens showed no signs of infection either clinically or in the histopathology. All materials tested produced lesions at the bone-implant interface. A significant difference was seen between metal injected vs. vehicle control animals and aluminium oxide injected vs. vehicle controls. Particles of stainless steel produced the greatest response and this finding may have implications for the use of metal on metal articulations aimed at eliminating polyethylene wear.