Biologic activity of wear particles.

Aseptic loosening resulting from periprosthetic osteolysis continues to be an important cause of hip implant failure. Wear particles from the bearing surfaces play a major role in initiating periprosthetic osteolysis, which is also potentiated by mechanical factors such as increased synovial fluid pressure. The precise mechanisms by which wear particles induce periprosthetic osteolysis have not been fully elucidated and remain an active subject of research. Particle characteristics such as composition, size, shape, and number (especially for particles in the most biologically active, submicrometer-size range) are recognized to significantly affect the overall cell and tissue response. The production of corrosion products, especially from metal-on-metal implants, also is a clinically significant issue, and individual variability in innate and adaptive immune responses is important but not yet completely defined. Because of the increasing need to implant hip prostheses in younger and more active patients, a better understanding of the biologic activity of wear particles from bearing couples is critical in the attempt to modulate the clinical effects of these particles and to develop materials with improved wear and corrosion resistance.