Understanding the Biomechanics of Shearing in Traumatic Brain Injury
Understanding the biomechanics of the neck from injury is crucial for diagnosing and treating TBI. Getting hit straight on, the way a woodpecker moves it's head, will be less damaging than being hit from the side where the neck can twist, causing tearing of white matter connections.
We're looking at the biomechanics of shearing in traumatic brain injury. If we're focused totally on the helmet, we're missing a lot about the biomechanics if we don't incorporate the neck because the head is moving back and forth. One analogy I like to make is that woodpeckers don't get concussions because they're going dead on. And so there's no shearing of the brain when they're hitting directly on. In fact, they've done studies with the NFL showing that players that get hit directly on are much less likely to get a concussion than if you get hit in the side of the head. So the side of the head, if you start moving, look at the neck. You start moving and then there's this shearing occurring. And there have been some very nice experiments actually at Washington University in St. Louis by Dr. Bailey where he's actually taken subjects in the MRI and they've just dropped just a little bit, and they can see the frontal lobes expanding and contracting, this shearing that's occurring in the front part of the brain, just with a little bit of rotation. So if you take that up several magnitudes, you can see how this expansion would tear white matter connections and produce many of the symptoms that people with concussion have. So here's the sort of anatomical, behavioral, and also neurophysiological if you include EEG or fMRI and so on, but these are the kind of things that go together in terms of a hypothesis that can be tested and also, if it turns out to be true, you can come up with diagnostics and therapeutics once we understand the science behind it. But I think that the biomechanic part would be great just to prevent all this from happening anyway. It's like back in the days before cars had seat belts and airbags. Seat belts and airbags have dramatically reduced injury--huge-- and it's because understanding the biomechanics of injury. They've been focused on merely bodily injury. Of course you don't fly out of the car anymore, you don't hit the windshield, and so that reduces brain injury. But you still have the person inside the car going like this and so on. The whole issue of getting head restraints and so on, they do that in NASCAR with the HANS device. They basically hold the helmet back to the car so there is no rotation of the head, and indeed, brain injuries have dropped dramatically in NASCAR and Formula 1 racers because of the HANS device. That's an extreme, right? So now there's no rotation of the head with respect to the torso. Let's take that somewhere in between where maybe there is some rotation but it's dampened. So we have to look at the biomechanics of the neck, and we're not going to solve this problem until we do that.
Posted on BrainLine March 1, 2012.
Jamshid Ghajar, MD, PhD is chief of Neurosurgery at Jamaica Hospital-Cornell Trauma Center, clinical professor of Neurosurgery at Weill Cornell Medical College and president of the Brain Trauma Foundation.
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