Quantifying the Importance of Active Muscle Repositioning a Finite Element Neck Model in Flexion Using Kinematic,...

Area of Science:

• Biomechanics
• Computational Modeling
• Injury Biomechanics

Background:

• Non-neutral neck positions are critical initial conditions in impact events, often linked to increased injury rates.
• Current finite element (FE) neck models typically use applied boundary conditions (BCs) for repositioning, which may not fully replicate in vivo muscle activity.
• In vivo, neck muscles actively contract to achieve and maintain head and neck posture, generating intrinsic loads.

Purpose of the Study:

• To compare a novel muscle-based repositioning method against traditional applied boundary conditions (BCs) in a contemporary FE neck model.
• To evaluate the impact of these different repositioning methods on forward head flexion of 30°.
• To assess the accuracy of kinematic and tissue-level responses.

Main Methods:

• A finite element neck model was utilized for forward head flexion simulation.
• The boundary condition (BC) method involved applying an external moment (2.6 Nm) to the head with the first thoracic vertebra (T1) fixed.
• The muscle-based method simulated co-contraction of neck flexor and extensor muscles under gravity loading to achieve the target 30° flexion.

Main Results:

• The muscle contraction method yielded a kinematic response within 10% of in vivo experimental data, outperforming the BC method (18% difference).
• Intervertebral disc forces calculated using muscle contraction (167 N compression, 12 N shear) were consistent with literature values, unlike the BC method which underpredicted forces.
• Muscle contraction led to a 60% average increase in annulus fibrosus strains across all levels compared to the BC method.

Conclusions:

• The muscle repositioning method significantly enhances the kinetic response and tissue-level outcomes in FE neck models compared to conventional BCs.
• Active muscle repositioning provides a more accurate simulation of in vivo neck kinematics and kinetics.
• These findings underscore the importance of incorporating active muscle function for realistic FE neck model simulations of non-neutral positions.