Pediatric Series

The Measure of a Child

Pediatric Anthropometrics & Their Impact on Wheelchair Design

child with measuring tape


Children are not just smaller versions of adults — a vital truth that seating and mobility manufacturers need to consider when designing any optimal pediatric seating or mobility system.

A 1998 report by the Association for the Advancement of Automotive Medicine noted that infants and children “differ structurally from the adult in a number of ways,” and added that infants and children also differ from each other: “Body size proportions, muscle bone and ligamentrus strengths are different,” the study noted.

Consider the proportions of an infant: At birth, its head is very large compared to the baby’s overall length. A baby’s head grows, but not as quickly or as much as the rest of the baby’s body. Therefore, by the time that baby is a toddler, his head-to-body proportions have changed. And that ratio continues to evolve as the child grows. When a typically developing child reaches adulthood, his head length-to-body length ratio is very different than when he was born.

Imagine, then, the problems that can arise if an adult wheelchair or seating system is simply “shrunken” to accommodate a child’s or infant’s height.

Body Structures Are Different for Babies & Children

The Automotive Medicine Study — conducted to review how children’s bodies differed from adults’ bodies in the context of automobile safety design — noted that a newborn typically weighs about 5 percent of what he/she will weigh as an adult. For the first nine months of life, a baby’s body fat increases rapidly. “After this period of high incremental change,” the study said, “there is a period of less rapid growth, so that by 5 years of age, the thickness of the subcutaneous layer is about half the thickness of the 9-month-old infant.”

Automotive manufacturers and companies that design children’s car seats need to know this information so they position safety restraints most effectively: “Loading of the body by straptype restraints must occur in areas where the body is strongest, i.e., on solid skeletal elements,” the study said. Likewise, seating and mobility manufacturers need to understand the specific anatomy of children to design optimal systems.

Gabriel Romero, VP of Sales & Marketing for Stealth Products, remembered the considerations that went into designing the company’s Niño system years ago.

“It was really important to create a product that was designed specifically for kids and early intervention, when it came to pads and the way they curved, how laterals fit,” he said. “We had to shrink everything down, but we also had to change some function on it. The swingaway didn’t swing away the way it needed to; the way it needed to swing away would be a different angle for a child.”

It’s a fact that Romero said has carried over to Stealth’s components, as well.

“I used to call it the Willy Wonka Machine,” he said. “Everybody wants to put the product through and just shrink it, and they think that’s enough. But it’s not, in cushions and especially positioning products. We encountered it in our belt line, since we have both adult sizes and pediatric sizes. We saw the cuts, the thicknesses of padding, all these differences. The padding is in a different place, and also the thickness of padding is different. You start looking at how the pelvis is different from an adult to a child and where the joints are, and it’s all different.”

ADI pediatric back

To maintain the appropriate contour in this ADI pediatric back, engineers had to consider the placement and thickness of the foam.

As an example, he showed off an ADI backrest (pictured) specially created for a young child to use on a self-propelled chair. “It had a contour, and I’m thinking I could cradle a baby with this back in my arms, as small as it is. But we didn’t only shrink it down. We had to shrink the contour, we had to design the foam differently — because if [the foam] was too thick, you wouldn’t have the contour.

“The point of contour is different because of the location of their arms. The last thing you want is to not consider where that drop in contour needs to be on a back, and how it could expand the child’s arms out so they’re really not getting a full push.”

Pediatric Growth Is Different

Josh Tucker, the new National Sales Manager for Leggero, pointed out that while kids and adults can both “grow,” the nature of the changes in size is different.

“The most important reason for a pediatric-specific design is going to be growth,” he said. “The [adult] body eventually stops growing in height. We can get wider, but our bone size stays the same. It doesn’t matter if I’m 6'2" and 300 lbs. or 6'2" and 170 lbs.; my skeletal structure is exactly the same. Children are not the same. Their hands and feet are growing, their legs are getting longer, their weight is getting higher. So when you take an adult version and just make it smaller, you’re not taking into account that the pediatric body is going to eventually grow out of that chair in every dimension.”

The means of everyday mobility can also impact a person’s body over time, Romero noted.

“If someone’s been in a wheelchair up to the age of 25, there are extreme differences between him and someone who was injured at 25 and then started using a wheelchair,” he said.

Camber for Kids

One area in which manual, self-propelled pediatric chairs can have a real-world advantage over their grownup counterparts is camber.

Camber can improve stability and maneuverability in both adult and pediatric manual chairs. But adding negative camber — i.e., angling the tops of the rear wheels towards the user’s body — also results in splaying the bottoms of the rear wheels outward. In an adult wheelchair, camber can therefore result in a chair that’s too wide to get through tight doorways, aisles and other small spaces.

On a kid’s chair that’s much narrower to begin with, adding camber and creating a greater width poses less of an accessibility problem. At the same time, angling the tops of the rear wheels toward a pediatric user can help kids reach, grab and push the wheel or pushrim more effectively, so they get more distance from each stroke.

And that’s important because in addition to children’s arms being shorter, they also have less strength than adults do.

“Taking into account the endurance of the child is also important,” Tucker said. “Children fade fast throughout the day, so we have to make sure pediatric equipment has push handles or handlebars, something for Mom and Dad to use.”

Creating Kid-Friendly Chairs

Push handles give parents a way to lend part-time propulsion assistance; anti-tippers are another way to make sure kids can feel free to explore in their self-propelled chairs while still being safe.

“Another thing to be considered is the activity level of the child,” Tucker confirmed. “Are they self propelling, or do Mom and Dad need to push? If they’re self propelling, do we have the ability to change the center of gravity and the rear wheel size as they grow? That creates a more controlled and safer ride; we don’t want them tipping out of their chairs.”

Another notable difference between adult and pediatric clients is how successfully a clinician, ATP or technician can communicate with them. For example, maybe it’s possible to explain the functionality of positioning components to a 30-year-old client. But if a 3-year-old doesn’t like the look of those components, you probably won’t win that argument.

“They’re very reactionary,” Tucker said of kids. “So aesthetics are a huge factor. Children are sensitive, and all children want to be included. When a child has mobility equipment that fits their personality, it makes them feel more confident and outgoing. They have people coming up to them saying, ‘Cool chair!’ They’re getting smiles and high-fives. It brings a lot of positive attention when it’s more aesthetically pleasing.”

And the impact doesn’t stop there.

“It’s important for Mom and Dad, too,” Tucker acknowledges. “For the parents, functionality, durability and the quality of the equipment are most important. Given the choice of pushing around something that looks like medical equipment or pushing around equipment that looks like it was made specifically for a child, they’re going to choose the latter. And we, as adults, can be sensitive, too. We don’t want people staring at our child or staring at us when we’re rolling by. So if the child is smiling, and the child is comfortable and confident, it makes the parents feel that way. When you put a kid into a position they don’t want to be in, they’re going to start crying and drawing attention to themselves. So why not put them into something that’s bright and comfortable and fits their personality?”

Creating Family-Friendly Chairs

Comfortable, confident kids go a long way toward creating comfortable, confident parents who are more likely to comply with clinicians’ recommendations for specialized seating and positioning. Ultimately, that overall impact can mean the difference between, for example, parents using a mainstream stroller purchased at a big-box store or instead using an adaptive stroller with optimal positioning components.

“Think about structure and positioning and infants,” Romero said. “[Infancy] is when they can start to develop some of these deformities. Imagine riding in a stroller and not having that structure and positioning. What starts to happen with the body? This is where it’s really important to have those points of positioning for an infant that’s growing into a youth and hopefully continuing as they become adults.”

Getting infants and young children into adaptive strollers with positioning components is critical enough, Romero said, that he would like to see RESNA standards on the subject.

“I’m okay with having a [standard] stroller to put your child into so you can quickly go to see the doctor,” he said, “as long as their daily-use [vehicle] is a positioning stroller. If their daily-use device is just a non-positioning stroller, then I have an issue. I see this at Abilities Expos: strollers they got at Costco and makeshift [positioning]. It’s still not specific to what their needs are.”

That’s a point of education, Romero added, that still needs to be strengthened.

“I learned a long time ago not to judge families who have children with disabilities,” he said. “A lot of times, we can do a better job of education. We can say, ‘If you’re not addressing [the child’s needs] through early-intervention positioning, this is what we’ve seen can happen.’

“I look forward to us working harder on this as an industry. If we know the journey, if the journey is clear early on, we need to go with preventive solutions from the beginning.”

Editor’s Note: “An Overview of Anatomical Considerations of Infants and Children in the Adult World of Automobile Safety Design,” Association for the Advancement of Automotive Medicine, can be found at the U.S. National Library of Medicine, National Institutes of Health:

This article originally appeared in the September 2018 issue of Mobility Management.

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