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3D Finite Element Modeling of Cervical Musculature and its Effect on Neck Injury Prevention
KTH, School of Technology and Health (STH), Neuronic Engineering.
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 [en]
Finite Element, Cervical Musculature, Neck injury prediction, Continuum Mechanics, Solid Elements
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-9503ISBN: 978-91-7415-180-0 (print)OAI: oai:DiVA.org:kth-9503DiVA: diva2:114241
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
List of papers
1. The importance of muscle tension on the outcome of impacts with a major vertical component
Open this publication in new window or tab >>The importance of muscle tension on the outcome of impacts with a major vertical component
Show others...
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
Keyword
finite elements, cervical muscles, impacts, head-neck kinematics, neck injuries
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9496 (URN)10.1080/13588260802215510 (DOI)000259036900003 ()2-s2.0-51449087120 (Scopus ID)
Note
QC 20100809Available from: 2008-11-10 Created: 2008-11-10 Last updated: 2017-12-14Bibliographically approved
2. Electromyography of Superficial and Deep Neck Muscles During Isometric, Voluntary, and Reflex Contractions
Open this publication in new window or tab >>Electromyography of Superficial and Deep Neck Muscles During Isometric, Voluntary, and Reflex Contractions
Show others...
2007 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 129, no 1, 66-77 p.Article in journal (Refereed) Published
Abstract [en]

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) front the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (in) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry, on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating,forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.

Place, publisher, year, edition, pages
ASME, 2007
Keyword
muscle activity; kinematics; numerical model validation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9497 (URN)10.1115/1.2401185 (DOI)000243778300009 ()2-s2.0-34248163533 (Scopus ID)
Note
QC 20100809Available from: 2008-11-10 Created: 2008-11-10 Last updated: 2017-12-14Bibliographically approved
3. Evaluation of a combination of continuum and truss finite elements in a model of passive and active muscle tissue
Open this publication in new window or tab >>Evaluation of a combination of continuum and truss finite elements in a model of passive and active muscle tissue
2008 (English)In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 11, no 6, 627-639 p.Article in journal (Refereed) Published
Abstract [en]

The numerical method of finite elements (FE) is a powerful tool for analysing stresses and strains in the human body. One area of increasing interest is the skeletal musculature. This study evaluated modelling of skeletal muscle tissue using a combination of passive non-linear, viscoelastic solid elements and active Hill-type truss elements, the super-positioned muscle finite element (SMFE). The performance of the combined materials and elements was evaluated for eccentric motions by simulating a tensile experiment from a published study on a stimulated rabbit muscle including three different strain rates. It was also evaluated for isometric and concentric contractions. The resulting stress-strain curves had the same overall pattern as the experiments, with the main limitation being sensitivity to the active force-length relation. It was concluded that the SMFE could model active and passive muscle tissue at constant rate elongations for strains below failure, as well as isometric and concentric contractions.

Place, publisher, year, edition, pages
London: Taylor & Francis, 2008
Keyword
Finite Element, muscle, material model, Hill-type material
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9494 (URN)10.1080/17474230802312516 (DOI)000260571300004 ()2-s2.0-58749116115 (Scopus ID)
Note
QC 20100809Available from: 2008-11-10 Created: 2008-11-10 Last updated: 2017-12-14Bibliographically approved
4. 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
Open this publication in new window or tab >>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
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
Keyword
FE modeling, cervical musculature, continuum elements, impact simulations
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9495 (URN)10.1097/BRS.0b013e31816b8812 (DOI)000254986500018 ()2-s2.0-42249108383 (Scopus ID)
Note
QC 20100809Available from: 2008-11-10 Created: 2008-11-10 Last updated: 2017-12-14Bibliographically approved
5. Neck Muscle Load Distribution in Lateral, Frontal, and Rear-end Impacts: A Three-Dimensional Finite Element Analysis
Open this publication in new window or tab >>Neck Muscle Load Distribution in Lateral, Frontal, and Rear-end Impacts: A Three-Dimensional Finite Element Analysis
2009 (English)In: Spine, ISSN 0362-2436, E-ISSN 1528-1159, Vol. 34, no 24, 2626-2633 p.Article in journal (Refereed) Published
Abstract [en]

Study Design. A finite element (FE) model of the human neck was used to study the distribution of neck muscle loads during multidirectional impacts. The computed load distributions were compared to experimental electromyography (EMG) recordings.

Objective. To quantify passive muscle loads in nonactive cervical muscles during impacts of varying direction and energy, using a three-dimensional (3D) continuum FE muscle model.

Summary of Background Data. Experimental and numerical studies have confirmed the importance of muscles in the impact response of the neck. Although EMG has been used to measure the relative activity levels in neck muscles during impact tests, this technique has not been able to measure all neck muscles and cannot directly quantify the force distribution between the muscles. A numerical model can give additional insight into muscle loading during impact.

Methods. An FE model with solid element musculature was used to simulate frontal, lateral, and rear-end vehicle impacts at 4 peak accelerations. The peak cross-sectional forces, internal energies, and effective strains were calculated for each muscle and impact configuration. The computed load distribution was compared with experimental EMG data.

Results. The load distribution in the cervical muscles varied with load direction. Peak sectional forces, internal energies, and strains increased in most muscles with increasing impact acceleration. The dominant muscles identified by the model for each direction were splenius capitis, levator scapulae, and sternocleidomastoid in lateral impacts, splenius capitis, and trapezoid in frontal impacts, and sternocleidomastoid, rectus capitis posterior minor, and hyoids in rear-end impacts. This corresponded with the most active muscles identified by EMG recordings, although within these muscles the distribution of forces and EMG levels were not the same.

Conclusion. The passive muscle forces, strains, and energies computed using a continuum FE model of the cervical musculature distinguished between impact directions and peak accelerations, and on the basis of prior studies, isolated the most important muscles for each direction.

Keyword
Finite Element, cervical musculature, impact biomechanics, muscle load, EMG
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9499 (URN)10.1097/BRS.0b013e3181b46bdd (DOI)000271884700005 ()2-s2.0-72849123527 (Scopus ID)
Note
QC 20100809. Uppdaterad från submitted till published (20100809). Tidigare titel: Neck Muscle Load Distribution in Lateral, Frontal, and Rear-end Impacts: a 3D Finite Element AnalysisAvailable from: 2008-11-10 Created: 2008-11-10 Last updated: 2017-12-14Bibliographically approved
6. Development of an active solid neck muscle FE model and its influence on neck injury prediction
Open this publication in new window or tab >>Development of an active solid neck muscle FE model and its influence on neck injury prediction
(English)Manuscript (Other academic)
Keyword
Finite Element, cervical musculature, muscle activation, neck injury prediction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9500 (URN)
Note
QC 20100809Available from: 2008-11-10 Created: 2008-11-10 Last updated: 2010-08-09Bibliographically approved

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