The effects of irradiation dose on the stiffness of cartilage grafts

Various centers report irradiated cartilage graft absorption rates that differ quite widely. We postulated that a major factor governing this phenomenon might be irradiation dose. Irradiation produces collagen cross- binding and increased resistance to absorption of such material when implanted. Since cross-binding produces stiffening of collagen, cartilage grafts were exposed to increasing doses of irradiation and their elastic modulus was measured. The postulate was that increasing radiation doses will produce grafts of increasing stiffness. Sternal cartilage, harvested from horses, was cut into blocks of a standard size and irradiated to 4, 6, 8, and 10 megarads. The elastic modulus of each specimen and matched control were measured on an Instron flexural testing machine (Instron Corp, Canton, MA). Irradiation at all four doses reduced the elastic modulus of the cartilage grafts, with the lowest dose producing a reduction of 50% and the highest dose one of 90%. High-dose irradiation appears to lesson greatly the stiffness of cartilage grafts and may be responsible for increasing absorption of grafts in centers in which high doses are used.