| 1. |
- Brolin, Karin, et al.
(author)
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Development of a finite element model of the upper cervical spine and a parameter study of ligament characteristics
- 2004
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In: Spine. - 0362-2436 .- 1528-1159. ; 29:4, s. 376-385
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Journal article (peer-reviewed)abstract
- Study Design. Numeric techniques were used to study the upper cervical spine. Objectives. To develop and validate an anatomic detailed finite element model of the ligamentous upper cervical spine and to analyze the effect of material properties of the ligaments on spinal kinematics. Summary of Background Data. Cervical spinal injuries may be prevented with an increased knowledge of spinal behavior and injury mechanisms. The finite element method is tempting to use because stresses and strains in the different tissues can be studied during the course of loading. The authors know of no published results so far of validated finite element models that implement the complex geometry of the upper cervical spine. Methods. The finite element model was developed with anatomic detail from computed tomographic images of the occiput to the C3. The ligaments were modeled with nonlinear spring elements. The model was validated for axial rotation, flexion, extension, lateral bending, and tension for 1.5 Nm, 10 Nm, and 1500 N. A material property sensitivity study was conducted for the ligaments. Results. The model correlated with experimental data for all load cases. Moments of 1.5 Nm produced joint rotations of 3degrees to 23degrees depending on loading direction. The parameter study confirmed that the mechanical properties of the upper cervical ligaments play an important role in spinal kinematics. The capsular ligaments had the largest impact on spinal kinematics (40% change). Conclusions. The anatomic detailed finite element model of the upper cervical spine realistically simulates the complex kinematics of the craniocervical region. An injury that changes the material characteristics of any spinal ligament will influence the structural behavior of the upper cervical spine.
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| 2. |
- Hedenstierna, Sofia, 1976-, et al.
(author)
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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
- 2008
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In: Spine. - : Lippincott Williams & Wilkins. - 0362-2436 .- 1528-1159. ; 33:8, s. E236-E245
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Hedenstierna, Sofia, 1976-, et al.
(author)
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Neck Muscle Load Distribution in Lateral, Frontal, and Rear-end Impacts : A Three-Dimensional Finite Element Analysis
- 2009
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In: Spine. - 0362-2436 .- 1528-1159. ; 34:24, s. 2626-2633
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Pernold, G., et al.
(author)
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Neck/shoulder disorders in a general population. Natural course and influence of physical exercise : A 5-year follow-up
- 2005
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In: Spine. - : Ovid Technologies (Wolters Kluwer Health). - 0362-2436 .- 1528-1159. ; 30:13, s. E363-E368
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Journal article (peer-reviewed)abstract
- Study Design. A 5-year follow-up study was conducted of men and women seeking care for new incidents of neck/shoulder disorders (NSD). Objectives. To study the natural course of pain and disability caused by NSD during a 5-year follow-up and to investigate the possible influence of regular physical exercise on recovery. Summary of Background Data. NSD are a major health problem, but their natural course is not very well studied. Several studies have investigated the role of physical exercise on NSD, with inconsistent results. Methods. At baseline, a total of 439 subjects seeking care for NSD completed a questionnaire, and were interviewed about personal, medical, and occupational history, as well as physical exercise during leisure time. Over 5 years, 4 follow-up assessments were made by postal questionnaire. At all measuring points, pain intensity ratings and disability scores were compared between men and women, and between 3 exercise categories. Results. The highest improvements in pain and disability, both in men and in women, were seen after 3 months. After that, only minor improvements were seen. In some cases, there was deterioration. However, after 5 years, both men and women had significant improvements, men more than women. Only the women were analyzed concerning physical exercise and were pooled into 3 categories according to intensity of exercise. There were no differences in changes in pain intensity and disability scores from baseline between the groups. Conclusions. A gender difference was seen in the change of pain and disability, with men having higher improvement than women over 5 years. Self-reported physical exercise of any intensity was not associated with higher recovery in women.
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