Tonic Finite Element Model of the Lower Limb

[+] Author and Article Information
Michel Behr, Pierre-Jean Arnoux, Thierry Serre, Lionel Thollon, Christian Brunet

Laboratoire de Biomécanique Appliquée, UMRT24 INRETS/Université de la Méditerranée, Faculté de Medecine secteur nord, Bld Pierre Dramard, 13916 Marseille, France

J Biomech Eng 128(2), 223-228 (Oct 25, 2005) (6 pages) doi:10.1115/1.2165700 History: Received February 08, 2005; Revised October 25, 2005

It is widely admitted that muscle bracing influences the result of an impact, facilitating fractures by enhancing load transmission and reducing energy dissipation. However, human numerical models used to identify injury mechanisms involved in car crashes hardly take into account this particular mechanical behavior of muscles. In this context, in this work we aim to develop a numerical model, including muscle architecture and bracing capability, focusing on lower limbs. The three-dimensional (3-D) geometry of the musculoskeletal system was extracted from MRI images, where muscular heads were separated into individual entities. Muscle mechanical behavior is based on a phenomenological approach, and depends on a reduced number of input parameters, i.e., the muscle optimal length and its corresponding maximal force. In terms of geometry, muscles are modeled with 3-D viscoelastic solids, guided in the direction of fibers with a set of contractile springs. Validation was first achieved on an isolated bundle and then by comparing emergency braking forces resulting from both numerical simulations and experimental tests on volunteers. Frontal impact simulation showed that the inclusion of muscle bracing in modeling dynamic impact situations can alter bone stresses to potentially injury-inducing levels.

Copyright © 2006 by American Society of Mechanical Engineers
Topics: Simulation , Muscle , Braking , Force
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Figure 1

Geometry acquisition process, from MRI images analysis to 3-D reconstruction

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Figure 2

Meshing of skeletal muscles. The muscle passive mass component is modeled with viscoelastic solids merged to a set of action lines.

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Figure 3

Schematic illustration of the contraction unit. δ is the instantaneous length of the muscle, A0 the level of activation, and Ta the time of activation.

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Figure 4

Sled acceleration and speed in a frontal impact, from (9)

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Figure 5

Resulting force at insertions for a fully relaxed muscle

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Figure 6

Resulting force at insertions for a fully braced muscle

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Figure 7

Simulated force recorded on the brake pedal (solid) and mean experimental maximal force exerted by volunteers (dashed)

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Figure 8

Simulated joint torques recorded during the emergency braking simulation (solid), and mean maximal joint torques recorded on volunteers (dashed)

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Figure 9

Frontal impact simulation with braced lower limb muscles

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Figure 10

Stress distribution (von Mises) as a function of muscle state, at t=85ms

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Figure 11

Illustration of the CU’s toggling phenomenon, for high deformation and activation levels




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