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 the hypothesis that the matching of the material modulus to that of cortical bone will result in an optimal stress transfer to the bone, resulting in a minimal bone loss. The biomechanical data showed no statistical difference in strain transfer in the bone before or after implantation of low modulus stems. The clinical reports of a number of earlier "isoelastic" devices showed evidence of loosening and lack of stability. The current interest has been in the development of femoral components made from carbon fiber reinforced polyaryletherketone, polysulfone, and carbon/carbon composites. As these materials are optimized, it is important to look into matching the rigidity of bone. Moreover, the unsupported neck area needs to be as strong as metal, like Ti6-Al4-V, to prevent failure, whereas the femoral component inside the bone needs 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.