Finite element micro-modelling of a human ankle bone reveals the importance of the trabecular network to mechanical performance: new methods for the generation and comparison of 3D models.

Most modelling of whole bones does not incorporate trabecular geometry and treats bone as a solid non-porous structure. Some studies have modelled trabecular networks in isolation. One study has modelled the performance of whole human bones incorporating trabeculae, although this required considerable computer resources and purpose-written code. The difference between mechanical behaviour in models that incorporate trabecular geometry and non-porous models has not been explored. The ability to easily model trabecular networks may shed light on the mechanical consequences of bone loss in osteoporosis and remodelling after implant insertion. Here we present a Finite Element Analysis (FEA) of a human ankle bone that includes trabecular network geometry. We compare results from this model with results from non-porous models and introduce protocols achievable on desktop computers using widely available softwares. Our findings show that models including trabecular geometry are considerably stiffer than non-porous whole bone models wherein the non-cortical component has the same mass as the trabecular network, suggesting inclusion of trabecular geometry is desirable. We further present new methods for the construction and analysis of 3D models permitting: (1) construction of multi-property, non-porous models wherein cortical layer thickness can be manipulated; (2) maintenance of the same triangle network for the outer cortical bone surface in both 3D reconstruction and non-porous models allowing exact replication of load and restraint cases; and (3) creation of an internal landmark point grid allowing direct comparison between 3D FE Models (FEMs).

Toward integration of geometric morphometrics and computational biomechanics: new methods for 3D virtual reconstruction and quantitative analysis of Finite Element Models.

The ability to warp three-dimensional (3D) meshes from known biological morphology to fit other known, predicted or hypothetical morphologies has a range of potential applications in functional morphology and biomechanics. One of the most challenging of these applications is Finite Element Analysis (FEA), a potentially powerful non-destructive tool in the prediction of mechanical behaviour. Geometric morphometrics is another typically computer-based approach commonly applied in morphological studies that allows for shape differences between specimens to be quantified and analysed. There has been some integration of these two fields in recent years. Although a number of shape warping approaches have been developed previously, none are easily accessible. Here we present an easily accessed method for warping meshes based on freely available software and test the effectiveness of the approach in FEA using the varanoid lizard mandible as a model. We further present new statistical approaches, strain frequency plots and landmark point strains, to analyse FEA results quantitatively and further integrate FEA with geometric morphometrics. Using strain frequency plots, strain field, bending displacements and landmark point strain data we demonstrate that the mechanical behaviour of warped specimens reproduces that of targets without significant error. The influence of including internal cavity morphology in FEA models was also examined and shown to increase bending displacements and strain magnitudes in FE models. The warping approaches presented here will be useful in a range of applications including the generation and analysis of virtual reconstructions, generic models that approximate species means, hypothetical morphologies and evolutionary intermediaries.