BIOMATERIALS ORTHOPEDIC APPLICATION PRECL INICAL AND CLINICAL-EVALUATION

It is very challenging to insure long term security and effectiveness for joint arthroplasties, artificial ligaments, extensive bone replace ment and some other orthopaedic biomaterials. How can we predict the l ong term security and efficacy of such an implant ? Only an interdisci plinary approach can provide a satisfactory answer. The surgeon must d efine 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 mechanica l resistance. This has to be performed in close connection with the bi omechanics lab. Biomechanic Science must predict the expected stresses . It has to design special simulator to quantify in vitro material tou ghness, wear characteristics, lubrication, behaviour and surface defor mation. Biological and mechanical standardized tests have to be carrie d on. Then it is possible to conduct a clinical trial, prospectively i n comparison to another already developed material. Clinical studies c ould serve to measure efficacy and radiological modification. After fa ilure, it is possible to analyse retrieved specimen, to measure the ma terial degradation in real environment, to perform biological studies on retrieved tissues ie : macrophagic activities, tissue response, bon e ingrowth, inflammatory or immulogical reaction. For more than twenty years we worked on alumina against alumina total hips. The idea was t o develop a low debris system to enhance long term longevity of the pr osthesis. The Charnley design has proven its effectiveness for more th an fifteen years, but polyethylene wear is responsible for late failur es. This is specially crucial for young patients, male sex and high ac tivity level patients. At the beginning, biological studies and mechan ical tests were performed, it appeared that the biological tolerance o f alumina ceramic was excellent, the fracture thoughness was adequate, but there were some problems related to alumina fixation in the body and also alumina head fixation on metallic stem. Alumina material impr oved with time. It was possible to diminish the fracture risks and to increase the safety. Parallel information from the first period was us ed 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 pro ved to be as safe as Charnley total hips. It has been proved to give b etter results in the young age population. Then it is now possible to operate on very young patients, to allow these patients to perform hea vy work, sports and regular daily activity for their demand. In conclu sion, long terme evaluation of orthopaedic implants has to be carried on with very scientific bases. Prospective tests must mimic a in-livin g system, but the clinical trial is the only way to really get the ans wer for the very long term.