Sunday, May 17, 2020

A single shake is dangerous

Babies are at far greater risk of brain damage than previously thought.

Even activities that seem innocent, like a quick run in a jogging stroller, can inflict abusive head trauma. And head injuries often go entirely undetected, so parents unwittingly repeat the same harmful behaviors over and over again.

These conclusions, which come from a new study I co-authored in the Journal of Pediatric Neurology, must be used to better educate new parents and inform manufacturers as they design car seats, safety helmets, and the like.

Abusive head trauma, or AHT, is typically referred to as --"shaken baby syndrome" -- the consequence of awful, deliberate abuse. Every year, an estimated 1,300 infants suffer this brain trauma. Roughly one in four tragically dies. Of those who survive, about 80 percent develop lifelong disabilities.

Of course, the overwhelming majority of parents would never intentionally harm their children. But, as our new research makes clear, it's possible to inflict AHT without even knowing it.

There are several reasons why this unsettling truth is just now coming to light. For starters, it's difficult to diagnose AHT. Some cases result in noticeable injuries, including bone fractures. But others result in far milder symptoms, such as fussiness. Many victims of AHT show no signs of trauma whatsoever. 

Plus, studying the biomechanics of AHT -- what physically occurs inside a child's skull when his or her head moves back and forth rapidly -- presents its own challenges. After all, there's no ethical way to observe or replicate such injuries in a scientific setting.

But thankfully, there's another way to study the problem. My colleagues and I used computer models to simulate the biomechanics of AHT. Specifically, we looked at how the cerebrospinal fluid cushions the brain when a child is shaken repeatedly.

What our models revealed is startling. Even at the lowest frequency we studied -- two shakes per second -- a single shake is dangerous. More troubling still, after that initial shake, the cerebrospinal fluid stops cushioning the brain altogether, causing the child’s brain to collide with the skull wall.

In other words, it doesn't take a violent act of frustration to damage a baby's brain. Something as ordinary as playfully tossing a child in the air or jogging with a baby could be enough to inflict severe head trauma. 

Of course, additional research is needed to develop even more precise AHT simulations. But our conclusions suggest several strategies for preventing head trauma in young children.

The first is simple -- parents must avoid any activity that shakes their infant's head even once, however harmless it might seem.

Just as important, designers should rely on biomechanical models when designing items like car seats, strollers, and other baby products. In 2018 alone, U.S. emergency rooms treated children under five for 59,000 injuries related to nursery products -- such as walkers, bouncer seats, and baby swings. Strollers were involved in 8,200 of those injuries. And across all of these incidents, the child's head was the most commonly injured part of the body.

Of course, faulty design didn't cause all of these accidents. But better-constructed products based on the latest biomechanics research could go a long way toward reducing head injuries in young children. Such research might reveal that jogging strollers require better shock absorbers, or that car seats should include more protective headgear.

At the very least, researchers should use biomechanical simulations to evaluate the safety of existing baby products. The results might surprise them -- newer products are not necessarily safer than older ones. In February, biomechanics researchers at Duke University found that World War I-era combat helmets provided better protection from certain kinds of explosions than current military helmets. Imagine what researchers might find if they subjected modern baby products to the same scrutiny.

The latest biomechanics research reveals that babies are far more vulnerable to head trauma than previously thought. It's time to minimize this trauma -- or eliminate it -- by using these findings to better educate new parents and design safer baby products.

Milan Toma, Alfonso Dehesa-Baeza , Rosalyn Chan-Akaley, Paul D. H. Nguyen, Hallie Zwibel. Cerebrospinal Fluid Interaction with Cerebral Cortex during Pediatric Abusive Head Trauma.  Journal of Pediatric Neurology.  DOI: 10.1055/s-0040-1708495

Abusive head trauma is the leading cause of fatal brain injuries in children younger than 2 years. It is a preventable and severe form of physical child abuse often linked to the forceful shaking of an infant or toddler. Victims of abusive head trauma can suffer permanent neurological damage, resulting in developmental delay and disability. The long-term effects of abusive head trauma are difficult to diagnose and predict. In this model, we use a high-order finite element method paired with the most comprehensive and current head/brain model and next-generation smoothed particle hydrodynamics. This is one of the first fluid–structure interaction frameworks that uses fluid material properties to represent the cerebrospinal fluid (CSF) while including all major anatomical features of the brain. The interaction of CSF with the brain cortex during abusive head trauma is demonstrated during multiple shaking cycles. A comprehensive and precise model that calculates for the role of CSF in neurological trauma will be useful both in the prevention and treatment of abusive head trauma and the determination of prognosis and patient outcomes.

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