(EDMONTON) As the song goes, the head bone is connected to the neck bone. Testing how sports helmets protect brains means you have to look beyond both head and helmet. You have to account for the unsung factor in head injury: the delicate-looking and flexible apparatus that is the human neck. And that’s where mechanical engineering master’s student Megan Ogle is training her focus.
“Basically, the biomedical community has found that the rotation of your head on your neck is a primary factor for concussion in sports,” she says.
Ogle is in the lab, pointing to a dummy head that is attached to a tower, which runs floor-to-ceiling. The model head is designed to measure impact when dropped from different heights on the tower. “In helmet testing situations, the dummy head is attached to the tower by a stiff metal rod,” she says. “These commercially available surrogate neck models are the only artificial necks that labs use right now—they’re built for automotive crash test dummies, which is not completely appropriate for head impact and helmet assessment,” Ogle says.
She explains that, when you take a hit, the motion of your head is dictated in part by your neck. To design accurate methods to study helmet effectiveness, we need a neck that realistically mimics the motion of a human neck. Under the co-supervision of Chris Dennison and Jason Carey, Ogle set about studying cadaveric necks and designing an artificial one with more natural human flex and stretch.
The necks she has been designing are based on a typical North American man in the 50th percentile for height and weight. “Once we demonstrate that it works, the neck model can be customized for women and children, too,” Ogle says.
In the meantime, her average guy’s test neck is flexible and does have a range of motion that is eerily lifelike. Made of putty-coloured silicone, inside there are simplified vertebrae made of aluminum, and intervertebral discs made of 3D-printed rubber. For stability, steel cables run through these and out the end of the model. The silicone represents the tissues of the neck. “Right now we’re building based on cadaver data,” she days, “which tells us the minimum bending requirements.”
The silicone neck is durable and can be used on the test tower many times—Ogle has used her current one in 50 tests and counting, and two more necks are in the works. She made earlier prototypes of clear ballistic gel, which make the inner workings clearly visible, but which didn’t stand up as well. Each neck could only be used five or six times before the quick-setting gel started to break down.
Ogle is testing the silicone neck, dropping it so it reaches speeds ranging from two metres per second to 5.5 metres per second. “The reason is that hockey helmets are tested at speeds of up to six metres per second,” Ogle says, “so if my neck holds out at those speeds it will be useful for testing those helmets.”
Ogle aims to have her human-like neck become a more accurate model than the stiff one used in automotive crash test dummies. With it, labs may one day be better equipped to perform realistic tests and collect data on helmet performance.