Strong similarities in the creep and damage behaviour of a synthetic bone model compared to human trabecular bone under compressive cyclic loading

Understanding the failure modes which instigate vertebral collapse requires the determination of trabecular bone fatigue properties, since many of these fractures are observed clinically without any preceding overload event. Alternatives to biological bone tissue for in-vitro fatigue studies are available in the form of commercially available open cell polyurethane foams. These test surrogates offer particular advantages compared to biological tissue such as a controllable architecture and greater uniformity. The present study provides a critical evaluation of these models as a surrogate to human trabecular bone tissue for the study of vertebral augmentation treatments such as balloon kyphoplasty. The results of this study show that while statistically significant differences were observed for the damage response of the two materials, both share a similar three phase modulus reduction over their life span with complete failure rapidly ensuing at damage levels above 30%. No significant differences were observed for creep accumulation properties, with greater than 50% of creep strains being accumulated during the first quarter of the life span for both materials. A significant power law relationship was identified between damage accumulation rate and cycles to failure for the synthetic bone model along with comparable microarchitectural features and a hierarchical composite structure consistent with biological bone. These findings illustrate that synthetic bone models offer potential as a surrogate for trabecular bone to an extent that warrants a full validation study to define boundaries of use which compliment traditional tests using biological bone.