Abstract
Introduction
Gamma Irradiation is often considered the gold standard for sterilizing bone allograft. However, a dose dependant decrease in the static mechanical properties of gamma irradiated bone has been well established. Supercritical Fluid Sterilization (SCF) using carbon dioxide represents a potential alternate method to sterilize allografts. This study aimed to evaluate the effect of SCF on the static and dynamic (fatigue) properties of cortical bone in 3-point bending.
Methods
Eighty paired 18-month old rabbit humeri were randomized to 4 treatments: Gamma Irradiation at 10 kGy or 25 kGy, SCF Control and SCF with Peracetic Acid (Figure 1) (n=20 pairs per group). One side was treated while the other acted as a control. Ten pairs in each group were tested statically at 5 mm/min; while ten were tested dynamically between 15–150 N at 4 Hz. Samples were fatigued to failure or 50000 cycles (run-out). All testing was performed at room temperature in a saline bath. A 2-tailed t-test was used to test for significance within pairs and a one-way ANOVA with Games-Howell post-hoc test was used to test between groups.
Results
There was a dose dependant decrease in both maximum load and energy to failure observed in the Gamma irradiated treatment groups in static 3 point bending (Figure 2). A dose of 10 kGy decreased the maximum load and energy by 12% and 26% respectively. While a dose of 25 kGy resulted in more substantial reductions of 18% (P = 0.02) and 44% (P = 0.005) respectively. Similarly, fatigue testing demonstrated a statistically significant (p < 0.05) dose dependant decrease in the fatigue properties of the bone following gamma irradiation (Figure 3).
Supercritical fluid treatment with or without additive had no significant effect on any of the measured mechanical parameters in 3-point bending. Furthermore, there was no significant change in fatigue behaviour following either SCF treatment.
No significant difference was detected between groups in the untreated control samples based on ANOVA. However, a statistically significant change was detected in the gamma irradiated samples between the 10 kGy and 25 kGy dose, and compared to both SCF groups. No statistical differences were detected between either SCF group.
Conclusions
Gamma irradiation at a low and standard dose compromised the static as well as the fatigue properties of the bone. This raises some concerns over the utility of gamma irradiation for load bearing allografts. SCF treatment has a bactericidal and virucidal effect [1, 2] and the results of this study demonstrate it maintains the mechanical integrity of bone in both static as well as dynamic loading.
