Ligament and tendon substitution with composite carbon fiber strands.

Carbon fiber strands were used experimentally to substitute for tendons in dogs and clinically to reconstruct tendons and ligaments in human. The investigation was carried out to determine the histologic appearance of the new composite structure and its tensile strength in comparison to the natural structure. The histologic picture disclosed a remarkable structure evolved by continuous irritation of the carbon fibers and consisting of two interrelated components: synthetic carbon fibers and biologic collagenous tissue. This carbon fiber composite structure was composed of long cylindrical units containing concentric layers of collagenous fibers and cells enveloping the core of each carbon fiber. After one year of physiologic use in dogs, the average ultimate tensile strength of the composite structure which replaced the quadriceps and triceps was 372 N, or 88% the strength of the natural tendons. One year after implantation the histologic picture of the composite structure in human showed a relatively dense collagenous architecture. However, a significant proportion of the structure was taken up by histiofibroblasts produced by the irritation of the carbon fibers. Thus, the density of the collagen in the composite structure remained relatively deficient in comparison to the nature tendon, and the structural tensile strength continued to depend entirely on the integrity of the carbon fibers.