The effect of gamma irradiation on the mechanical properties of human bone was examined. Specimens of cancellous bone were cut from the proximal epiphyseal region of fresh-frozen tibiae and divided into control and irradiated groups according to anatomical region. The irradiated groups were exposed to 10,000, 31,000, 51,000, or 60,000 gray (1.0, 3.1, 5.1, or 6.0 megarad). The specimens were tested in compression to failure to determine failure stress, strain to failure, and elastic modulus.
Failure stress and elastic modulus were found to be proportional to the square of the density and were normalized with respect to this property. Significant differences in normalized failure stress (p<0.001) and normalized elastic modulus (p = 0.003), when compared with the values for matched control specimens, were found only for the specimens that had been irradiated with 60,000 gray (6.0 megarad).
Clinical Relevance: These data suggest that compressive failure stress and elastic modulus of cancelbus tibial bone in humans decrease significantly when the bone is irradiated with 60,000 gray (6.0 megarad). However, these properties did not decrease significantly when the accepted dose for sterilization before allografting (25,000 gray 12.5 megaradl) was used.