BACKGROUND: Gamma radiation sterilization can make cortical bone allograft more brittle, but whether it influences mechanical properties and propensity to form microscopic cracks in structurally intact cancellous bone allograft is unknown. QUESTIONS/PURPOSES: We therefore determined the effects of gamma radiation sterilization on structurally intact cancellous bone mechanical properties and damage formation in both low- and high-density femoral cancellous bone (volume fraction 9%-44%). METHODS: We studied 26 cancellous bone cores from the proximal and distal femurs of 10 human female cadavers (49-82 years of age) submitted to a single compressive load beyond yield. Mechanical properties and the formation of microscopic cracks and other tissue damage (identified through fluorochrome staining) were compared between irradiated and control specimens. RESULTS: We observed no alterations in mechanical properties with gamma radiation sterilization after taking into account variation in specimen porosity. No differences in microscopic tissue damage were observed between the groups. CONCLUSIONS: Although gamma radiation sterilization influences the mechanical properties and failure processes in cortical bone, it does not appear to influence the performance of cancellous bone under uniaxial loading. CLINICAL RELEVANCE: Our observations support the use of radiation sterilization on structurally intact cancellous bone allograft.

HASH(0x32c12710)

Structurally intact cancellous bone allograft is an attractive tissue form because its high porosity can provide space for delivery of osteogenic factors and also allows for more rapid and complete in-growth of host tissues. Gamma radiation sterilization is commonly used in cancellous bone allograft to prevent disease transmission. Commonly used doses of gamma radiation sterilization (25-35kGy) have been shown to modify cortical bone post-yield properties and crack propagation but have not been associated with changes in cancellous bone material properties. The purpose of this study was to determine the effects of irradiation on the elastic and yield properties and microscopic tissue damage processes in dense cancellous bone. Cancellous bone specimens (13 control, 14 irradiated to 30kGy) from bovine proximal tibiae were tested in compression to 1.3% apparent strain and examined for microscopic tissue damage. The yield strain in irradiated specimens (0.93+/-0.11%, mean+/-SD) did not differ from that in control specimens (0.90+/-0.11%, p=0.44). No differences in elastic modulus were observed between groups after accounting for differences in bone volume fraction. However, irradiated specimens showed greater residual strain (p=0.01), increased number of microfractures (p=0.02), and reduced amounts of cross-hatching type damage (p<0.01). Although gamma radiation sterilization at commonly used dosing (30kGy) does not modify elastic or yield properties of dense cancellous bone, it does cause modifications in damage processes, resulting in increased permanent deformation following isolated overloading.

Human peripheral lymphocytes from tumor-bearing and non-tumor-bearing patients were added to monolayer cultures of autochthonous and allogeneic normal or neoplastic cells in vitro with or without phytohemagglutinin (PHA). The normal cells were derived from skin, the tumor cells from postnasal carcinomas or sarcomas. The cultures were scored for clearly visible plaques in the monolayer. Without PHA, lymphocytes affected autochthonous skin target cells in 1 of 16 cultures. If PHA was added,the figure increased to nearly 50%(12/28). Whether this phenomenon is related to an autoimmune reaction or to some less specific effect of the PHA stimulus is unknown at present. In the absence of PHA, lymphocytes from African tumor-bearing hosts destroyed allogeneic skin fibroblasts in 4 of 14 cases, and lymphocytes from non-tumor-bearing Swedish donors showed this effect in 14 of 24 tests. The somewhat lower reactivity of the African lymphocytes was also apparent in other tests. It cannot be stated whether the difference was due to the tumor-bearing condition of the hosts or to some other differences involved in comparison of the two groups. Without PHA, lymphocytes of the African tumor patients destroyed their own autochthonous tumor cultures in 4 of 16 cases. Addition of PHA increased the proportion of positives to 20 of 28. A comparison with the corresponding figures for autochthonous skin cultures (1/16 and 12/28, respectively) indicates a relatively higher reactivity against the autochthonous tumor cells, both with and without PHA. This cannot be interpreted as a difference in target cell sensitivity to the same lymphocyte action, because no such difference was apparent when the sensitivity of skin and tumor to allogeneic lymphocytes was compared in the absence of PHA (4/14 and 4/14 with African lymphocyte donors; 14/24 and 14/24 with Swedish lymphocyte donors, respectively). The most probable explanation is that the antigenic barrier responsible for the lymphocyte effect is larger for tumor than for skin, or that the results reflect a presensitization of the tumor donor against its autochthonous neoplastic cells.