The effect of sterilization on the dynamic mechanical properties of paired rabbit cortical bone.

The optimal sterilization method for load bearing allografts remains a clinical concern. Recently, supercritical carbon dioxide (SCCO2) treatments have been shown to be capable of terminally sterilizing a range of bacteria and viruses, while preserving the static mechanical properties of cortical bone. This study evaluated the effect of SCCO2 treatment compared with two doses of gamma irradiation, on clinically relevant dynamic mechanical properties of cortical bone. Quasi-static testing was also performed to compare the impairment of treatment. Whole paired adult rabbit humeri were dissected and randomly assigned into either SCCO2 Control, SCCO2 Additive or gamma irradiation at 10 or 25kGy treatment groups. The bones were treated and mechanically tested in three-point bending, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated from static tests. The number of cycles to failure was determined for fatigue at 6-60% of the ultimate load. This study found that SCCO2 treatment with or without additive did not alter static or dynamic mechanical properties. Gamma irradiation had a deleterious dose dependent effect, with statistically significant (p<0.05) reductions in all static mechanical parameters at 25kGy. This effect was increased in fatigue with statistically significant decreases in both the 10 and 25kGy dose groups. This study highlights the expediency of SCCO2 treatment for load bearing bone allograft processing as terminal sterilization can be achieved while maintaining both the quasi-static and dynamic mechanical properties of the graft.