Head-first impacts are dangerous because the neck is required to suddenly stop the motion of the torso immediately after the head stops. The combination of the torso mass and speed can exceed the strength of the neck in this scenario.
Existing helmet designs are effective when protecting against skull and brain injury using hard outer shells and internal padding, but they do not provide any additional protection against injury to the neck.
Pro-Neck-Tor™ makes use of a double-shell design with engineered mechanical guides connecting the two shells. During a head-first impact, Pro-Neck-Tor™ guides the head along the surface, reducing the neck's need to stop the following torso, minimizing the loads on the neck during impact. Proof-of-concept tests using an instrumented mechanical head and neck model have demonstrated that Pro-Neck-Tor™ can reduce neck loads in head-first impact.
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"The Pro-Neck-Tor™ helmet induces head motion along an engineered path in either forward or backward direction by guiding the inner shell relative to the outer shell."
In a head-first impact, a person's head strikes the ground and is stopped almost instantly while their torso is still moving. During these few milliseconds, there is almost zero load passing through the neck. If the head is sufficiently "gripped" by the impact surface such that it is unable to move, then the neck is forced to absorb the incoming momentum of the torso.
There are many factors that influence neck injury development in head first impacts. These include: posture of the neck at impact, the incoming velocity, the alignment between the impact surface, the incoming force, and the 'axis' of the spine, and the "constraint" upon the head at impact. The degree of constraint on the head depends on factors such as the friction between the head/helmet and impact surface and the compliance of the impact surface. The most dangerous posture is when the head is flexed forward approximately 30° which removes the natural curvature of the spine. The worst case scenario would be when someone with this straightened posture hits head-first into a low stiffness and high friction surface that is perpendicular to the neck axis. In this situation, there is nowhere for the energy from the torso to go except into strain energy in the spinal column. As the neck is very stiff in compression, large forces develop over small displacements that are large enough to fracture the spinal column leaving it unstable and vulnerable to spinal cord injury as further motion ensues.
A more favorable set of impact conditions would be if the head were to hit a low friction, stiffer surface that is oblique with respect to the axis of the spine as opposed to perpendicular. This allows the head to keep moving along the impact surface as force is transferred through the neck. By moving the head along the impact surface, the spine is forced into a posture less prone to an axial column-like response and more likely to a bending response. This allows for energy to be dissipated into the soft tissues of the neck as the head moves and rotates along the impact surface. Research with cadaveric head and neck specimens has shown that this can help to avoid neck injury in impacts with sufficient impact speed to cause injury with other more constraining boundary conditions1.
The Pro-Neck-Tor™ helmet induces head motion along an engineered path in either forward or backward direction by guiding the inner shell relative to the outer shell. This allows the head to move along the surface and reduces the neck loads as described above and as shown in the sequence of images below.
To understand the Pro-Neck-Tor™ technology and how it works to prevent cervical spinal cord injuries we can first review the way in which state-of-the-art helmets (left) work. A standard helmet has a hard outer shell to spread the force onto the helmet padding while the padding deforms during an impact to protect the wearer against skull and brain injury. This design has proven effectiveness when it comes to protecting against skull and brain injury, but unfortunately it provides little protection for the wearer's neck in head-first impacts. The Pro-Neck-Tor™ double shell design and the guide between the inner and outer shells can be seen at left. It should be mentioned that traditional helmets are not generally designed to protect against neck injuries but the Pro-Neck-Tor™ helmet is designed to offer this protection in addition to the head protection normally associated with safety helmets.
"Helmets designed around the Pro-Neck-Tor™ technology behave exactly like existing helmets except in a head first impact"
The Pro-Neck-Tor™ technology will induce head motion if and only if a certain force threshold is reached at the interface between the shells. This means that helmets designed around the Pro-Neck-Tor™ technology should behave exactly like existing helmets except in a head-first impact. Pro-Neck-Tor™'s design is still under development, but many proof-of-concept tests using mechanical models of the head and neck (including the Hybrid III crash test dummy head show in the images at left) have been carried out by scientists and engineers in the Orthopaedic and Injury Biomechanics Group at The University of British Columbia. In these tests Pro-Neck-Tor™ helmet prototypes (including prototypes incorporated into ski and football helmets, see images below) reduced neck loads by up to 59% in head-first impacts over a range of impact conditions when compared to head-first impacts with standard versions of the corresponding helmets.
Pro-Neck-Tor™ prototype incorporated into a commercial ski helmet with data from lower neck compressive loads in a head first impact with and with out the Pro-Neck-Tor™ prototype.
Pro-Neck-Tor™ prototype incorporated into a commercial football helmet with data from lower neck compressive loads in a head first impact with and with out the Pro-Neck-Tor™ prototype.
Nightingale RW, McElhaney JH, Richardson WJ, et al. Dynamic response of the head and cervical spine to axial impact loading. Journal of Biomechanics 1996;29:307-18.