Towards a neck injury prevention helmet for head-first impacts : a mechanical investigation

Cervical spine and spinal cord injuries (SCI) have catastrophic and permanent neurological consequences and are known to occur from head-first impacts in many activities where helmets are worn. A particularly dangerous posture for catastrophic cervical SCI from head-first impacts occurs when the head is flexed (nodded) approximately 30 degrees downward such that the cervical spinal column becomes aligned. In this posture, the neck reacts axially along its stiffest axis such that high forces develop over small displacements. The deceleration of the torso creates strain energy in the vertebrae beyond their tolerance. It has been shown that increasing constraint on the head at impact places the cervical spine at greater risk of injury compared to less constraining head conditions that allow the head to rotate and translate along the impact surface. At impact speeds near the tolerance for injury, this degree of head constraint can make the difference between avoiding neck injury altogether or the development of unstable neck fractures. This thesis involves the design, construction, and testing of a mechanical head, neck, and a helmet prototype that induces horizontal motion to the head as a neck injury mitigation approach in aligned column head-first impacts. In addition, a new in vitro cervical spine model of head-first impact was developed. All testing utilized a free standing drop tower to create an experimental model of the head, neck and torso system. The head and neck model exhibited an impact response that was in good agreement with the in vitro human response and was sensitive to surface compliance and platform angle. The lower-neck, head, and impact surface were instrumented to provide estimates of impact severity. The helmet prototype, of realistic size, mass, and inertia, showed that when the induced head motion acted to increase the obliqueness of the impact, a combined injury metric comprised of peak neck axial force and peak bending moment was reduced by 30% to 51% compared to testing without induced head motion. These reductions in lower-neck reaction loads were achieved without significant increases, or accompanying decreases in head accelerations. This work is being used to develop and test subsequent helmet prototypes.Applied Science, Faculty ofGraduat