Characterisation and Validation of Sawbones™ Artificial Composite Femur material

Sawbones 4th Generation composite bones are useful tools for the mechanical testing of orthopaedic devices and validation of FE models. The products are intended to provide more reliability and less variability than cadaveric specimens, and have been often used in biomechanical analyses. However, no independent validation of these data exists. Three point bending tests on the cortical component of the femur and on sheets of the same material were conducted in separate independent laboratories to determine the Young’s modulus of the material. These data were incorporated into a FE model of a femur to be validated against an equivalent mechanical test using both force-displacement and strain gauge data. There was significant inter-sample variability in Young’s modulus, potentially due to microstructural heterogeneity. All samples were significantly less stiff than the quoted value of 16.0 GPa (Sawbones 2014), with a mean Young’s modulus of 10.7 GPa calculated for the cortical sample and 8.4 GPa for the sheets. The FE model compared favourably with the mechanical testing, with a 3.3% higher stiffness than that recorded experimentally, giving confidence in our Young’s modulus data. This paper has highlighted that that care must be taken when employing these products as substitutes for cadaveric specimens.