Abstract
Background: Musculoskeletal models served to analyze head-neck motion and injury during automotive impact. Although muscle activation is known to affect the kine- matic response, a model with properly validated muscle contributions does not exist to date. The goal of this study was to enhance a musculoskeletal neck model and to validate passive properties, muscle moment arms, maximum isometric strength, and muscle activity. Methods: A dynamic nonlinear musculoskeletal model of the cervical spine with 48 de- grees of freedom was extended with 129 bilateral muscle segments. The stiffness of the passive ligamentous spine was validated in flexion/extension, lateral bending, and axial ro- tation. Instantaneous joint centers of rotation were validated in flexion/extension, and mus- cle moment arms were validated in flexion/extension and lateral bending. A linearized static model was derived to predict isometric strength and muscle activation in horizontal head force and axial rotation tasks. Results: The ligamentous spine stiffness, instantaneous joint centers of rotation, muscle moment arms, cervical isometric strength, and muscle activation patterns were in general agreement with biomechanical data. Taking into account equilibrium of all neck joints, iso- metric strength was strongly reduced in flexion (46 %) and axial rotation (81 %) compared to a simplified solution only considering equilibrium around T1-C7, while effects were marginal in extension (3 %). Conclusions: For the first time, isometric strength and muscle activation patterns were accurately predicted using a neck model with full joint motion freedom. This study demon- strates that model strength will be overestimated particularly in flexion and axial rotation if only muscular moment generation at T1-C7 is taken into account and equilibrium in other neck joints is disregarded.
Highlights
The complex anatomy of the human neck allows for high flexibility in rotation and translation through seven cervical vertebrae controlled by over 70 muscles
The largest model discrepancy was found in the C2–C1 joint during axial rotation, where the model had a considerably smaller neutral zone (a 10 degrees range compared to 50 degrees in the experiment) and was unable to perform the expected large axial rotation
This study shows that a moment balance over the entire spine must be considered when calculating muscle activation and cervical strength
Summary
The complex anatomy of the human neck allows for high flexibility in rotation and translation through seven cervical vertebrae controlled by over 70 muscles. This high level of complexity has made it difficult for scientists to understand load distributions occurring in the cervical spine. In vitro research has made properties available related to the anatomy and passive loading of the neck, it has proven difficult to obtain in vivo data of the deep cervical tissues from experiments. The goal of this study was to enhance a musculoskeletal neck model and to validate passive properties, muscle moment arms, maximum isometric strength, and muscle activity
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