Finite Element Analysis of Cervical Spine Kinematic Response during Ejection Utilising a Hill-Type Dynamic Muscle...

Area of Science:

• Biomechanics
• Spinal Injury Prevention
• Aerospace Medicine

Background:

• Pilot ejection seats involve high accelerations that can cause neck injuries.
• Understanding the role of active neck muscles in mitigating these injuries is critical.
• Previous studies often modeled neck muscles as passive or omitted them.

Purpose of the Study:

• To investigate the impact of active neck muscle engagement on cervical spine dynamics during simulated emergency ejections.
• To compare the rotational responses of cervical spine segments with active, passive, and no muscle models.
• To identify critical muscle dynamics influencing injury risk.

Main Methods:

• A detailed 3D finite element (FE) model of the cervical spine (C0-T1) was developed, incorporating 13 major neck muscles.
• Active muscle forces were simulated using a Hill-type model, considering muscle state, velocity, and length.
• A simulated ejection acceleration profile (125 G·s⁻¹, peak 10 G) was applied to the model.

Main Results:

• Active muscles increased flexion motion in the upper cervical segments (C0-C2) compared to passive or no muscle models.
• Cervical spine segments showed similar S- and C-curvature trends, with peak flexion around 95-105 ms.
• Active muscle activity generally reduced rotational angle variability across segments, except for C0-C2 between 60-120 ms.

Conclusions:

• Active muscle dynamics are crucial in determining muscle force magnitudes during ejection.
• Conscious muscle contraction by pilots before ejection is vital for reducing cervical spine injury risk.
• The findings highlight the importance of including active muscle properties in biodynamic simulations for pilot safety.