[Orthopedic biomaterials].

It is very challenging to insure long term security and effectiveness for joint arthroplasties, artificial ligaments, extensive bone replacement and some other orthopaedic biomaterials. How can we predict the long term security and efficacy of such an implant? Only an interdisciplinary approach can provide a satisfactory answer. The surgeon must define the needs, he must find the appropriate surgical techniques and conduct the clinical trial. The material scientist must elaborate safe and secure materials with regards to their biotolerance and mechanical resistance. This has to be performed in close connection with the biomechanics lab. Biomechanic Science must predict the expected stresses. It has to design special simulator to quantify in vitro material toughness, wear characteristics, lubrication, behaviour and surface deformation. Biological and mechanical standardized tests have to be carried on. Then it is possible to conduct a clinical trial, prospectively in comparison to another already developed material. Clinical studies could serve to measure efficacy and radiological modification. After failure, it is possible to analyse retrieved specimen, to measure the material degradation in real environment, to perform biological studies on retrieved tissues i.e. : macrophagic activities, tissue response, bone ingrowth, inflammatory or immunological reaction. For more than twenty years we worked on alumina against alumina total hips. The idea was to develop a low debris system to enhance long term longevity of the prosthesis. The Charnley design has proven its effectiveness for more than fifteen years, but polyethylene wear is responsible for late failures. This is specially crucial for young patients, male sex and high activity level patients. At the beginning, biological studies and mechanical tests were performed, it appeared that the biological tolerance of alumina ceramic was excellent, the fracture toughness was adequate, but there were some problems related to alumina fixation in the body and also alumina head fixation on metallic stem. Alumina material improved with time. It was possible to diminish the fracture risks and to increase the safety. Parallel information from the first period was used to increase the material quality, the surgical techniques and also to define indication in the use of such material. It is now clear and it also has been published that alumina against alumina system has proved to be as safe as Charnley total hips. It has been proved to give better results in the young age population. Then it is now possible to operate on very young patients, to allow these patients to perform heavy work, sports and regular daily activity for their demand.(ABSTRACT TRUNCATED AT 400 WORDS)