[Total arthroplasty: the other surfaces; wear and tear and osteolysis]

Total replacement remains a successful solution for degenerative, inflammatory and postraumatic diseases in large joints. This treatment has considerably improved the quality of life of the patients. Despite recent innovations in biomaterials, implant design and surgical technique, there are still failures, most of them related to wear at the surface of some component. Particles are generated that produce inflammatoty and osteolytic reactions leading to implant loosening. In that case, revision surgery is mandatory to remove and substitute the worn component. The operation is far more difficult and costly, has a higher rate of complications and a worse outcome that the initial surgery. This general review of the problem is focused on the specific features of wear particles and the cellular and molecular mechanisms of the biological reactions in the osteoclastic and osteoblastic pathways. Osteolysis is described as a pathological modification of normal bone remodeling with the interaction between osteoblasts and osteoclasts as the main feature. We include some contributions of our laboratory at H U La Paz. Having reached an advanced identification of the molecular factors involved in wear osteolysis, many research groups are trying to develop potential "biologic" (non surgical) therapies for the prevention and treatment of bone loss.