THE APPLICATION OF NEW COMPOSITE-MATERIALS FOR TOTAL JOINT ARTHROPLASTY

The material and design issues for the composite hip stem development are examined. The development of the ''isoelastic'' hip is based on th e hypothesis that the matching of the material modulus to that of cort ical bone will result in an optimal stress transfer to the bone, resul ting in a minimal bone loss. The biomechanical data showed no statisti cal difference in strain transfer in the bone before or after implanta tion of low modulus stems. The clinical reports of a number of earlier ''isoelastic'' devices showed evidence of loosening and lack of stabi lity. The current interest has been in the development of femoral comp onents made from carbon fiber reinforced polyaryletherketone, polysulf one, and carbon/carbon composites. As these materials are optimized, i t is important to look into matching the rigidity of bone. Moreover, t he unsupported neck area needs to be as strong as metal, like Ti6-Al4- V, to prevent failure, whereas the femoral component inside the bone n eeds to have lower rigidity. Therefore, monolithic composite material from neck area to the distal stem will not withstand the loading needs and a material optimization scheme is required to come up with a long -lasting composite device. Lastly, the price vs. patient benefits for these composite material stems need to be established.