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The importance of muscle tension on the outcome of impacts with a major vertical component
KTH, School of Technology and Health (STH), Neuronic Engineering.
KTH, School of Technology and Health (STH), Neuronic Engineering.
KTH, School of Technology and Health (STH), Neuronic Engineering.
Center for Applied Biomechanics, University of Virginia, Charlottesville.
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2008 (English)In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 13, no 5, 487-498 p.Article in journal (Refereed) Published
Abstract [en]

The hypothesis that muscle tension protects the spine from injuries in helicopter scenarios was tested using a finite-element model of the human head and neck. It was compared with cadaver crash sled experiment with good correlation. Then, simulations were performed with a sinusoidal velocity (5-22 G) applied at T1 60° to the horizontal plane. The model with relaxed muscle activation had delayed and decreased peak head rotation compared with passive properties only. Full muscle activation decreased the injury risk for the 13.5-22 G impacts. A sensitivity study of the impact angle showed a very slight variation of the resulting neck flexion, and 1° change affected all ligament injury predictions less than 4%. Finally, simulations with helmets resulted in increased ligament and disc strains with increasing helmet mass and with an anterior or inferior shift of the centre of gravity. It is concluded that the hypothesis seems to hold.

Place, publisher, year, edition, pages
London: Taylor & Francis , 2008. Vol. 13, no 5, 487-498 p.
Keyword [en]
finite elements, cervical muscles, impacts, head-neck kinematics, neck injuries
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-9496DOI: 10.1080/13588260802215510ISI: 000259036900003Scopus ID: 2-s2.0-51449087120OAI: oai:DiVA.org:kth-9496DiVA: diva2:114230
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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