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Session: Musculoskeletal System
Session starts: Thursday 24 January, 10:40
Presentation starts: 11:40
Room: Lecture room 558

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Paul Klaver ()
Michiel Oosterwaal ()
Lodewijk van Rhijn ()
Cees Oomens ()
Kenneth Meijer ()

Abstract:
Recently, a new foot and ankle model has been developed (the Glasgow/Maastricht model), which can predict the effect of an insole during dynamic loading conditions [1]. The model can be made patient-specific by measuring the anatomical structures from CT scans. The mechanical properties of the plantar soft tissue then can be estimated by changing the properties in the model until good agreement between the deformations predicted by the model and measured from CT scans during loading is obtained. The purpose of this study was to test if this procedure can provide realistic results. For seven patients suffering from metatarsalgia and ten healthy participants CT scans of the foot were made [2]. Three CT scans of the subjects loaded right foot and one CT scan of the unloaded right lower leg were made. During loading, plantar pressure was measured with a pedar insole (Novel gmbh, Munich, Germany). The CT images were segmented with MIMICS (Materialise, Leuven, Belgium) and a 2D finite element mesh of the unloaded situation was generated (3-matic, Materialise, Leuven, Belgium). The force measured in the experiment was applied as boundary condition to the model using the finite element program FEBio [3]. The material properties of the tissue in the model then were updated until best agreement was found between experimental and model deformations. The preliminary results obtained in this study demonstrate that the estimation of material properties using this backward approach is feasible. A finite element model simulating a loaded foot was created with the Ogden model describing the soft tissue. Values for the model were taken from literature [4]. Simulation of the plantar pressure using this model showed an error of just 1 kPa in part of the heel in comparison to the pressure measurements in the loaded situation. However, in the other parts of the foot the pressure estimation was not that close, so the values taken from literature appear not suitable enough to describe soft tissue. In future work several components such as plantar fascia and the Achilles tendon will be added in order to get a better pressure distribution along the plantar tissue. The optimization routine will be used to find the material properties that result in the best agreement between CT data and the model, and are therefore more suitable to describe soft tissue. Also the validity of this method applied on the 3D situation will be studied in further research. 1. Oosterwaal M, Telfer S, Carbes S, Torholm S, Meijer K, Woodburn J, Rhijn Lv: Generation of a dataset to develop a subject-specific, multibody, finite element, dynamic foot model. In EUROMECH Colloquium 511. Ponta Delgada, Azores, Portugal; 2011. 2. Oosterwaal M, Telfer S, Torholm S, Carbes S, van Rhijn LW, Macduff R, Meijer K, Woodburn J: Generation of subject-specific, dynamic, multisegment ankle and foot models to improve orthotic design: a feasibility study. BMC Musculoskelet Disord 2011, 12:256. 3. Maas SA, Ellis BJ, Ateshian GA, Weiss JA: FEBio: Finite Elements for Biomechanics. Journal of Biomechanical Engineering, 134(1):011005, 2012 4. Erdemir A, Viveiros ML, Ulbrecht JS, Cavanagh PR: An inverse finite-element model of the heel-pad indentation. Journal of biomechanics, 39(7):1279-1286, 2006