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A 3D Continuum Finite Element Muscle Model for the Investigation of Cervical Spine Load-Sharing Mechanisms and Injury Assessment during Impact Loading Scenarios
- Author / Creator
- Moghaddam, Fatemeh
The mechanical behavior of the individual cervical tissues as well as the head-neck complex kinematics plays a very important role in proper functioning of the cervical spine and is a key factor in more appropriate understanding of injury mechanism, prevention, detection, control and treatment. This aids clinicians, engineers and other involved researchers to develop better detective, preventive and treatment techniques for cervical disorders. Although great efforts have been made to understand the biomechanics of the cervical spine tissues, and the cervical musculature in particular, many aspects are still challenge. The cervical musculature is the major stabilizer of the neck and head, and is composed of active and passive components. The majority of FE models have used discrete spring elements to simulate the muscles. These elements fail to represent mass inertia, and the real geometry of the muscles. Hence, computational 3D FE models have been proposed to overcome these limitations. Moreover, such 3D computational FE models can be a useful tool considering difficulties associated with in-vivo and in-vitro impact tests on human subjects.
The main objective of this study was to develop a 3D FE model of the cervical spine including a 3D continuum cervical musculature governed by a new material model. This material simulates both active and passive parts of the muscle. The muscle behavior was numerically formulated and a user defined FORTRAN subroutine, UMAT, was developed to implement the model into the software ABAQUS. In addition, 3D continuum cervical muscles constructed from Magnetic Resonance Images (MRI) were added to a detailed FE model of a Ligamentous Spine (LS). This is the first FE model of the cervical spine that has 3D musculature including both active and passive properties of the muscle governed by only one constitutive equation. This new thorough cervical spine model was used to investigate the overall kinematics of the head and neck as well as the mechanical responses of the individual cervical tissues. Moreover, the responses of the LS model and a spine with only Passive Musculature (PMS) were compared to the response of a spine with both active and passive musculature (FMS) to investigate the effect of the muscle activation on the behavior of the cervical spine during dynamic loading conditions. And finally, the concept of Strain Energy (S.E.) was used to investigate how spinal components interact together during a specific loading condition.
The obtained results indicated the important role of the cervical musculature and its active part in particular, in the cervical spine behavior under impact loading scenarios. Adding the passive musculature to the LS model not only restricted the movement of the head and neck, but also altered the stress and stress distribution in the cervical tissues. More importantly, adding the muscle activation to the spine model significantly reduced the head and neck range of motion, and, in consequence, improved the stability of the spine.
Additionally, the results of spinal load sharing analyses pointed out that the amount of S.E. in the spine during frontal impact scenarios was significantly greater than that during rear-end impact scenarios. In addition, the spinal load sharing results showed, regardless of the impact direction and severity, adding the muscle activation to the spine decreased the amount of S.E. absorbed by the spine.
Finally, the new continuum muscle model was able to predict strain, force, and energy distribution in the muscles and indicated which muscle bears the major role during a specific impact loading scenario. The results agreed with the experimental data (EMG) and previous numerical studies.
- Graduation date
- Fall 2018
- Type of Item
- Doctor of Philosophy
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