Does finite element simulation have a role to play in foot and ankle surgery?

E. Pegg, H. Chen, C. Brockett, A. Gulati, J. Mangwani

¹University of Bath, Department of Mechanical Engineering, Bath, United Kingdom

²University of Leeds, School of Mechanical Engineering, Leeds, United Kingdom

³Sandwell and West Birmingham NHS Trust, West Bromwich, United Kingdom

⁴University Hospitals of Leicester NHS Trust, Leicester, United Kingdom

Finite Element Analysis (FEA) can provide invaluable insight into the mechanical function of the joints and long bones. For the hip and knee numerous validated FEA models have been successfully developed to study forces, stress and strain patterns and to predict failure of implants. The foot and ankle complex, however, consists of multiple bones and articulations and is heavily reliant on soft tissues for stability with complex material behaviours. These features mean that such FEA simulations require more computational effort and expertise to simulate, which is a significant barrier to research in this area. Consequently very little progress has been made despite the potential of this methodology.
The goal of this research project is to facilitate the use of FEA of the foot and ankle through creation of an open-source ankle model, which could be mapped on to patient-specific scans. A preliminary model has been created using the open CT dataset: Visible Human Project Female (National Library of Medicine). The model was created using open-source FEA software, FEBio (University of Utah). Linear materials were assigned to the bones (E=7300MPa, ν=0.3, ρ=1730kg/m³) and cartilage (E=10MPa, ν=0.4, ρ=1100kg/m³). Spring elements were used to represent the ligaments with properties taken from Mondal et al. [1]. A standing load case was modelled, assuming even distribution of load between the feet, and the results match closely to published work.
This model is a promising first step and future work will incorporate more complexity to better represent the soft tissues, different patient geometries and load cases; which could revolutionise research into foot and ankle conditions. It will provide a valuable tool for simulating mechanical testing conditions on a human ankle joint without the necessity of complex, and often expensive, in-vitro or in-vivo experiments.
[1] Mondal et al. (2017). J Orthop, 14(3), 329–335.

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