An extended discrete element method for the estimation of contact pressure at the ankle joint during stance phase

Pressure distribution at the instant of maximum loading (78% of the stance).
EDEM is on the left, DEM on the right.

Abnormalities in the ankle contact pressure are related to the onset of osteoarthritis. In vivo measurements are not possible with currently available techniques, so computational methods are often used instead. The discrete element method (DEM) is a computational technique which models the articular cartilage as a bed of independent springs, assuming a linearly elastic behaviour and absence of relative motion between the bones. In this study, we present the extended DEM (EDEM) which is able to track the motion of talus over time. The method was used, with input data from a subject-specific musculoskeletal model, to predict the contact pressure in the ankle joint during gait. Results show that the motion of the talus had more effect on the extension and shape of the pressure distribution than it had on the magnitude of the pressure: EDEM predicted wider contact areas than DEM, and less uniform pressure distribution. We also evaluated the role played by the material properties of ankle ligaments and the geometry of the ankle cartilage, revealing that the thickness of the cartilage layers greatly influences the computed contact patterns.

Schematic pipeline of musculoskeletal model and EDEM

Benemerito, I., Modenese, L., Montefiori, E., Mazzà, C., Viceconti, M., Lacroix, D., Guo, L. (2020), “An extended discrete element method for the estimation of contact pressure at the ankle joint during stance phase”, Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, URL: https://doi.org/10.1177/0954411920905434 http://eprints.whiterose.ac.uk/156748/ 

Acknowledgements:

UK EPSRC (MultiSim project, EP/K03877X/1), European Commission (MD-PAEDIGREE project, FP7-ICT Programme, Project ID: 600932)