Does the immune system play a role in loosening and osteolysis of total joint replacements?

Total joint replacement is a highly successful surgical procedure with an excellent outcome over many years. However, because this procedure is now being performed in younger patients, and because the average age of our population continues to increase, greater expectations have been placed on joint implants in the hope that they will last forever. Aseptic loosening and osteolysis of total joint replacements are the main processes limiting long-term implant survival. This paper focuses on the possible role of immunological mechanisms in the processes of loosening and osteolysis of joint replacements, with special emphasis on polymeric materials. This topic is very controversial: In vitro experiments and in vivo studies in animals and humans are reviewed and provide evidence for both sides of the debate. In some patients, immunological processes appear to be activated after a total joint replacement has been implanted. Specific materials or their by-products might function as haptens and elicit a T-lymphocyte-mediated, delayed hypersensitivity reaction. Many factors probably are important, including the genetic makeup and immune competence of the patient, prior exposure to the same or similar materials, degree of exposure (rate of generation of particles and the efficacy of clearance mechanisms), and characteristics of the particles themselves.