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How does a three-dimensional continuum muscle model affect the kinematics and muscle strains of a finite element neck model compared to a discrete muscle model in rear-end, frontal, and lateral impacts
KTH, School of Technology and Health (STH), Neuronic Engineering.
KTH, School of Technology and Health (STH), Neuronic Engineering.
2008 (English)In: Spine, ISSN 0362-2436, E-ISSN 1528-1159, Vol. 33, no 8, E236-E245 p.Article in journal (Refereed) Published
Abstract [en]

STUDY DESIGN. A finite element (FE) model of the human neck with incorporated continuum or discrete muscles was used to simulate experimental impacts in rear, frontal, and lateral directions. OBJECTIVE. The aim of this study was to determine how a continuum muscle model influences the impact behavior of a FE human neck model compared with a discrete muscle model. SUMMARY OF BACKGROUND DATA. Most FE neck models used for impact analysis today include a spring element musculature and are limited to discrete geometries and nodal output results. A solid-element muscle model was thought to improve the behavior of the model by adding properties such as tissue inertia and compressive stiffness and by improving the geometry. It would also predict the strain distribution within the continuum elements. METHODS. A passive continuum muscle model with nonlinear viscoelastic materials was incorporated into the KTH neck model together with active spring muscles and used in impact simulations. The resulting head and vertebral kinematics was compared with the results from a discrete muscle model as well as volunteer corridors. The muscle strain prediction was compared between the 2 muscle models. RESULTS. The head and vertebral kinematics were within the volunteer corridors for both models when activated. The continuum model behaved more stiffly than the discrete model and needed less active force to fit the experimental results. The largest difference was seen in the rear impact. The strain predicted by the continuum model was lower than for the discrete model. CONCLUSION. The continuum muscle model stiffened the response of the KTH neck model compared with a discrete model, and the strain prediction in the muscles was improved.

Place, publisher, year, edition, pages
Lippincott Williams & Wilkins , 2008. Vol. 33, no 8, E236-E245 p.
Keyword [en]
FE modeling, cervical musculature, continuum elements, impact simulations
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-9495DOI: 10.1097/BRS.0b013e31816b8812ISI: 000254986500018Scopus ID: 2-s2.0-42249108383OAI: oai:DiVA.org:kth-9495DiVA: diva2:114228
Note
QC 20100809Available from: 2008-11-10 Created: 2008-11-10 Last updated: 2017-12-14Bibliographically approved
In thesis
1. 3D Finite Element Modeling of Cervical Musculature and its Effect on Neck Injury Prevention
Open this publication in new window or tab >>3D Finite Element Modeling of Cervical Musculature and its Effect on Neck Injury Prevention
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Injuries to the head and neck are potentially the most severe injuries in humans, since they may damage the nervous system. In accidents, the cervical musculature stabilizes the neck in order to prevent injury to the spinal column and is also a potential site for acute muscle strain, resulting in neck pain. The musculature is consequently an important factor in the understanding of neck injuries. There is however a lack of data on muscle response and little is known about the dynamics of the individual muscles. In this thesis the numerical method of Finite Elements (FE) is used to examine the importance of musculature in accidental injuries. In order to study the influence of a continuum musculature, a 3D solid element muscle model with continuum mechanical material properties was developed. It was hypothesized that a 3D musculature model would improve the biofidelity of a numerical neck model by accounting for the passive compressive stiffness, mass inertia, and contact interfaces between muscles. A solid element representation would also enable the study of muscle tissue strain injuries.

A solid element muscle model representing a 50th percentile male was created, based on the geometry from MRI, and incorporated into an existing FE model of the spine. The passive material response was modeled with nonlinear-elastic and viscoelastic properties derived from experimental tensile tests. The active forces were modeled with discrete Hill elements. In the first version of the model the passive solid element muscles were used together with separate active spring elements. In the second version the active elements were integrated in the solid mesh with coincident nodes. This combined element, called the Super-positioned Muscle Finite Element (SMFE), was evaluated for a single muscle model before it was incorporated in the more complex neck muscle model. The main limitation of the SMFE was that the serial connected Hill-type elements are unstable due to their individual force-length relationship. The instabilities in the SMFE were minimized by the addition of passive compressive stiffness from the solid element and by the decreased gradient of the force-length relation curve.

 The solid element musculature stabilized the vertebral column and reduced the predicted ligament strains during simulated impacts. The solid element compressive stiffness added to the passive stiffness of the cervical model. This decreased the need for additional active forces to reproduce the kinematic response of volunteers during impact. The active response of the SMFE improved model biofidelity and reduced buckling of muscles in compression. The solid element model predicted forces, strains, and energies for individual muscles and showed that the muscle response is dependent on impact direction and severity. For each impact direction, the model identified a few muscles as main load carriers that corresponded to muscles generating high EMG signals in volunteers. The single largest contributing factor to neck injury prediction was the muscle active forces. Muscle activation reduced the risk of injury in ligaments in high-energy impacts. The most urgent improvements of the solid element muscle model concerns: the stability of the SMFE; the boundary conditions from surrounding tissues; and more detailed representations of the myotendinous junctions. The model should also be more extensively validated for the kinematical response and for the muscle load predictions.

It was concluded that a solid muscle model with continuum mechanical material properties improves the kinematical response and injury prediction of a FE neck model compared to a spring muscle model. The solid muscle model can predict muscle loads and provide insight to how muscle dynamics affect spinal stability as well as muscle acute strain injuries.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vii, 60 p.
Series
Trita-STH : report, ISSN 1653-3836 ; 2008:6
Keyword
Finite Element, Cervical Musculature, Neck injury prediction, Continuum Mechanics, Solid Elements
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9503 (URN)978-91-7415-180-0 (ISBN)
Public defence
2008-12-05, 3-221, Alfred Nobels Allé 10, Huddinge, 13:00 (English)
Opponent
Supervisors
Note
QC 20100809Available from: 2008-11-17 Created: 2008-11-10 Last updated: 2010-08-09Bibliographically approved

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