Prosthetics/orthotics/devices
A 3-dimensional finite element model of the human foot and ankle for insole design

https://doi.org/10.1016/j.apmr.2004.03.031Get rights and content

Abstract

Cheung JT-M, Zhang M. A 3-dimensional finite element model of the human foot and ankle for insole design.

Objective

To investigate the effect of material stiffness of flat and custom-molded insoles on plantar pressures and stress distribution in the bony and ligamentous structures during balanced standing.

Design

A 3-dimensional (3-D) finite element model of the human ankle-foot complex and a custom-molded insole were developed from 3-D reconstruction of magnetic resonance images and surface digitization. The distal tibia and fibula, together with 26 foot bones and 72 major ligaments and the plantar fascia, were embedded in a volume of soft tissues.

Setting

Computational laboratory in a rehabilitation engineering center.

Participant

A healthy man in his mid twenties (weight, 70kg).

Interventions

Not applicable.

Main outcome measures

Foot-support interfacial pressure, von Mises stress in bony structures, and strain of the plantar fascia were predicted using the finite element model.

Results

A custom-molded, soft (Young modulus, E=0.3MPa) insole reduced the peak plantar pressure by 40.7% and 31.6% at the metatarsal and heel region, respectively, compared with those under a flat, rigid (E=1000MPa) insole. Meanwhile, a 59.7% increase in the contact area of the plantar foot was predicted with a corresponding peak plantar pressure increase of 22.2% in the midfoot.

Conclusions

The finite element analysis implies that the custom-molded shape is more important in reducing peak plantar pressure than the stiffness of the insole material.

Section snippets

Methods

The geometry of the finite element model was obtained from 3-D reconstruction of magnetic resonance (MR) images from the right foot of a healthy man in his mid twenties (height, 174cm; weight, 70kg). Coronal MR images were taken at intervals of 2mm in the neutral unloaded position. The images were segmented using MIMICS, version 7.10,a to obtain the boundaries of skeleton and skin surface. The boundary surfaces of the skeletal and skin components were processed using SolidWorks 2001b to form

Results

We constructed a 3-D finite element model of the human foot and ankle to study the effects that stiffness and shape of foot insole have on plantar pressure distribution, and to study the internal stresses in the bones during balanced standing. Figure 2 depicts the plantar pressure distribution obtained from the F-scan measurements and figure 3 gives the pressure distribution predicted by finite element simulation during balanced standing. Both the measured and predicted values showed high

Discussion

The predicted plantar pressure distribution pattern was, in general, comparable to the F-scan measurement. However, the predicted values of peak pressure were higher than the F-scan measurements. The difference may be caused by resolution differences between the F-scan measurement and the finite element analysis. Having a spatial resolution of about 4 sensors per cm2, the F-scan sensors recorded an average pressure for an area of 25mm2. By contrast, the finite element analysis provided

Conclusions

A geometric, detailed 3-D finite element model of the human foot and ankle was developed to estimate the plantar pressure and the internal stress and strain in the bony and soft tissue structures under various loading and supporting conditions. Finite element analysis indicated that the insole’s custom-molded shape is more important in reducing peak plantar pressure than the stiffness of the material from which it is made. A comprehensive, finite element, ankle-foot model makes monitoring the

Acknowledgment

We thank the Scanning Department of St. Teresa’s Hospital, Kowloon, Hong Kong, for facilitating the MR scanning.

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    Supported by the Hong Kong Jockey Club (endowment) and The Hong Kong Polytechnic University (research studentship and research grant G-T888).

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

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