Importance of Neck Boundary Condition and Posture on Cervical Spine Response Assessed using a Detailed Finite Element Human Model in a Head-First Impact.

Purpose: Head-first impacts (HFI) are associated with a high risk of cervical spine trauma. Experimentally, HFI use an inverted full body (FB), or a head and neck with torso surrogate mass (TSM) attached to the first thoracic vertebra. FB testing is complex and few studies have been completed, while more testing has been done in the TSM configuration, no comparison of the two setups exists.

Methods: In this study, the effect of TSM and FB on the head and neck response was investigated computationally using three initial neck postures (flexed, neutral, and extended). The TSM was applied to an extracted head and neck from a contemporary full body model, while the FB was used for comparison. The models were inverted and dropped on a rigid plate at three velocities (2.0, 3.1, and 3.6 m/s). Head impact force, head and neck kinetics, vertebral kinematics, and internal energy were measured and compared between the models.

Results: TSM models demonstrated higher neck forces, and internal energy, compared to FB models. Despite similar head contact forces, the compliant thorax of the FB model reduced the neck forces and energy. The neutral and extended posture predicted higher neck forces due to facet joints engaging, while anterior head translation in the flexed posture reduced neck forces.

Conclusions: This study identified that the neck response using a TSM boundary condition differs from a FB condition, leading to higher neck loads, and that lordotic neck postures lead to higher neck forces compared to a kyphotic initial posture.