Biomechanical comparison of bone recycling methods in an ovine cortical bone model

To perform a comprehensive biomechanical comparison of bone recycling methods (autoclaving, pasteurization, irradiation, and liquid nitrogen freezing) with the frozen allograft method using fresh ovine femora as a cortical bone model.

A total of 126 ovine femoral specimens with 2 mm cortical thickness and 20-25 cm length were harvested and allocated into six groups (n = 21 each): Control, autoclaving, pasteurization, irradiation, liquid nitrogen, and frozen allograft (stored at - 80 °C for 12 weeks) in vitro. Sterilization protocols were followed according to standard procedures. Each group was further divided into subgroups for biomechanical testing in three-point bending, axial compression, and torsion using the MTS Bionix 858 system. The outcome parameters included the maximum load, stiffness, energy to failure, and shear modulus. All tests were performed under identical conditions and repeated in triplicates to ensure reproducibility. Statistical analysis was performed using ANOVA with Tukey's post-hoc test. Post-hoc power analysis confirmed an adequate sample size. The Biomechanical Efficiency Index (BEI) was calculated by normalizing the bending, compression, and torsional stiffness values of each group to those of the control group.

Autoclaving produced the poorest biomechanical outcomes across all parameters, with significantly lower maximum load, stiffness, energy to failure, and shear modulus than those of all other groups (p < 0.001). The pasteurization and irradiation groups preserved mechanical properties moderately better than autoclaving but were significantly inferior to the liquid nitrogen and frozen allograft groups. Liquid nitrogen freezing preserved biomechanical strength most comparable to the control group, with no significant difference in three-point bending, compression, and torsion tests (p > 0.05). The liquid nitrogen group also demonstrated significantly higher stiffness and shear modulus than the autoclaving group (p < 0.001), confirming its superiority. The calculated BEI values for the control, liquid nitrogen, frozen allograft, pasteurization, irradiation, and autoclaving were 100%, 93%, 88%, 85%, 86%, and 53%, respectively.

Liquid nitrogen freezing and frozen allograft methods provide biomechanical properties closest to untreated bone and are preferable for biological reconstruction after tumor resection. Pasteurization and irradiation remain acceptable alternatives, whereas autoclaving should be avoided because of the severe deterioration of mechanical integrity.