Minimum Thresholds for Brain Injury--A Moving Target

We put out a newsletter called: Biomechanical Testimony: When Should it be Admitted?

It explained:

Biomechanical experts estimate force and acceleration at impact. But translating those estimates into brain (or other soft-tissue) injury predictions is intellectually dishonest on two levels.

First, there is the ecological fallacy. Population-level statistics don’t tell us whether an individual was injured. Estimates about force and acceleration don’t provide a jury any more insight into whether the plaintiff suffered a brain injury than race-based statistics from standardized testing do about whether a kid can do math problems or read a story.

Second, research has found no clear universal threshold of force for concussion. Some high-force impacts cause no concussion, while some concussions occur from low forces. Factors like impact direction, rotation of the head and individual susceptibility all influence whether an mTBI occurs.

I wanted to expand on the second point: there are no bright-line force numbers for when a concussion will or will not happen.

There are some studies (dating back to 2008) that attempt to measure the forces that football players experience in games and what adults and kids experience in everyday life.

Distillation of the college football research showed that college football players didn't suffer concussions more than 10 percent of the time at certain force levels.

Sometimes these forces lead to concussions. Most of the time they don't.

Let's put it in context with another statistic. Pedestrians hit by vehicles traveling 20 MPH have only a 5 - 10 percent chance of serious injury or death.

Can you imagine the defense, in a wrongful death case, parading out a biomechanical expert to testify that it must not have been the collision that killed Jack but that, statistically, he must have succumbed to some progressive/degenerative condition....

And with the other studies the only real takeaway is that further research is needed. There might be a "number" below which it's impossible for a concussion to occur, but we don't know what number (or combination of numbers) establishes that threshold value.

And even if we were to figure out a minimum threshold, that's only half the battle. The other half would be figuring out what forces the injured person experienced in the collision. Unless the injured person is outfitted with sensors in advance, it's impossible to measure.

Biomechanical experts who talk about the forces of everyday life aren't adding anything to the conversation. They are unable to offer testimony that really moves the needle in terms of whether a specific collision caused a specific person to suffer a concussion.

Until there is a threshold number and biomechanical experts are able to figure out whether that number was achieved in a specific collision, their testimony should be excluded in brain injury cases.