Through a complete review of published research over the last 60 years, researchers aim to propel development of new head injury metrics forward.
Metrics that help engineers design safer helmets and vehicles to prevent fatalities went mostly unchanged for about 50 years. Now, researchers are looking for better metrics to help prevent brain injuries—from mild concussions to traumatic damage.
In “A Review of Head Injury Metrics Used in Automotive Safety and Sports Protective Equipment,” published in the ASME Journal of Biomedical Engineering, authors Stefan Duma and Bethany Rowson examined every major metric that has been published over the past 60 years, including some of the original work done at Wayne State University in the 1960s and 1970s that examined skull fractures and were used for early football helmet and vehicle design standards. This effort summarizes existing head injury metrics and their applications for head and brain injuries.
Duma is Harry C. Wyatt Professor of Engineering and director of the Institute for Critical Technology and Applied Science (ICTAS) at Virginia Tech and Rowson is a former Virginia Tech research assistant professor. The team defined a metric as any variable or combination of variables that is “used to assess injury severity, while a criterion is any quantitative value that is considered a threshold for injury or is assigned a predicted risk of injury.”
The Virginia Tech team has about 30 years of history in automobile safety. About 20 years ago, they started working more in the sports and football area. Today, about 40 faculty and students at Virginia Tech work on brain-related research.
“When you look at brain injury, a lot of the same tools are used when we evaluate vehicle safety as well as athletic player safety,” Duma said. “So, it made a lot of sense for us to do a detailed systematic review of brain injury criteria and head injury criteria that are used in both auto safety and sports biomechanics.”
According to the review, the first head injury metrics to be included in safety standards were meant to reduce severe head injuries and fatalities. After the National Operating Committee on Standards for Athletic Equipment implemented football helmet standards in 1974, fatal head injuries in football dropped by approximately 74 percent, the authors noted. Similarly, with the implementation of mandatory Federal Motor Vehicle Safety Standards in 1968, the fatality rate of motor vehicle occupants dropped by 81 percent. Implementation of both standards saved thousands of lives, Duma added.
“When we started using some of these metrics, we had a big reduction in injury rates. But there was not a lot of change for about 50 years, so it kind of stayed steady,” he said. “And now we’re in a much more dynamic time where people are looking at much more complex and effective injury criteria. And the ultimate hope is that we can reduce more brain injuries.”
Duma and Rowson noted that injury metrics are based on translational motion, rotational motion, or a combination of the two, and figuring out how to limit the amount of energy that is transferred during an event to an individual’s head. Once metrics have been tested, evaluated, and analyzed, engineers are able to use them to better design cars and helmets that minimize injury and fatality risks.
While there have been numerous proposed brain injury metrics, the authors stated that few have been implemented in safety standards for vehicles or sports protective equipment. And those are still based off experimental data collected in the 1950s and 1960s, which was used to develop the Wayne State Tolerance Curve, which is the relationship between linear head acceleration, duration of acceleration, and incidence of head injury.
“If you start with reducing fatalities, which a lot of the initial work has done, now what we want to do is reduce concussions and brain injuries,” he said. “So, the real focus now and into the future is what metric is going to be best to help designers reduce concussion.”
A tremendous amount of research is already underway worldwide into concussions, but “there’s a great deal still to be discovered in that space and a lot of questions to answer, [such as] why there are different injury rates,” Duma said. “This paper can help provide the foundation to examine some of these trends by using some of these different metrics.”
But one major drawback to existing research is how limited the data is for different populations. Historically, most brain injury analysis in sports focused on male football players, Duma noted.
“For about the past five years, we’ve begun to focus much more on gender and sex differences in brain injury,” he said. “We’ve really expanded that effort into women’s lacrosse, rugby and soccer, really looking at understanding brain injury differences between men and women. And that’s where a lot of the research is right now.”
Duma and Rowson cautioned that as these new metrics are developed, they must be effectively evaluated against real world datasets without sampling bias, such as actual injury rates from a population, and head impact data from both high- and low-risk individuals.
“The thing that I’m really interested in is a simple question, which is how much is too much? How many times, how often, what’s the frequency, what’s the magnitude? We really just don’t know [the answer to] that simple question,” Duma explained. “So, the idea is if we can better determine that, then we can really start to scope firm limits on head impact exposure for all sports and all activities.”
