Mythbusters: Are bent legs in a car seat developmentally dangerous?


I had the great fortune of helping out at a fantastic car seat check event a few weeks back where I met with 4 different families. While their car seats and children could not have been more different, all 4 of them asked me the same question: isn’t having bent legs (while rear facing) bad for a child’s hips?

I see this quite a bit on the internet- inevitably whenever a news source writes about a new law or rear facing evidence, someone comments that sitting with the legs bent is going to forever stunt the growth of a child or cause hip dysplasia or otherwise damage a baby’s developing bones. So it seems like it’s time to delve into the research and maybe dust off my physical therapy degree.

Myth: Having legs bent or in a frogged position when rear facing can cause damage to the hip/knee joints and associated bones.

Quinn in Fllo rf

First, let’s look at hip dysplasia. This is obviously a concern for many parents of infants. Hip dysplasia occurs when the hip “socket” is not deep enough, typically at birth. This is common in babies who are breech, first babies and in multiples. When babies have dysplasia, the first line of treatment is a harness. This harness attaches to the baby’s trunk and a series of straps pull the hip into flexion and abduction, basically a frog leg position.

Which is oddly similar to how big kids sit while rear facing. So it stands to reason that if the child sits in the position a hip dysplasia harness would hold them in rear facing, that there’s no significant risk of hip dysplasia from extended rear facing. Also worth noting is that by the time kids reach the age where their legs are scrunched, they are typically standing/walking, which helps deepen that hip socket and vastly reduces the risk of hip dysplasia.

oliver rf bvct 1 Infant in a Pavlik Harness Source:

Okay, so I feel like we’re good on the dysplasia part. So what about bone growth?

Bones grow in response to pressure placed upon them. So when you stand, run, walk, it signals cells that build bone, to spring to action. When you don’t bear weight for a while, those cells don’t work, but the cells that break down bone still work like they’re supposed to- and thus, bone density decreases. But nothing about sitting in a car with legs bent, should change the rate of bone growth or absorption, nor should it place so much stress on a joint that bone would form in an incorrect direction or pattern.

Muscles also shorten and lengthen in response to use, but prolonged positioning is required for a muscle to shorten or lengthen and unless a child is riding in the car for days or weeks on end, without stretch breaks (which is not a very good idea, if that isn’t obvious), there’s virtually zero risk of muscle shortening or lengthening from rear facing.

The last leg concern I’ve heard is that children can get blood clots from rear facing because their legs are up. This is, and I want to be very clear, not at a concern at all. Blood is pumped out of the veins using “muscle pumps” or essentially the pressure that the muscles around the veins create whenever the legs are in use. Veins don’t pulse like arteries so they rely on the muscle action to move blood back to the heart. In children, the muscle pumps are active all day long because children, even those rear facing, never stop moving. Also, having the legs supported and not dangling like you would see in a forward facing child, actually makes it easier for the blood to return to the heart, thus actually reducing the risk of blood clots.

But most of all, I’d like to challenge you to watch children while at rest or play for about 15 minutes before you worry about this particular issue. I did this tonight with my older child during a 22 minute television show. In those 22 minutes, he fidgeted quite a bit, but he spent 20 of those minutes with his legs flexed and abducted, basically just like they would be in the car. Because that’s a very comfortable position for kids and doesn’t put stress on their joints or muscles.

Verdict: BUSTED

There’s just no reason why sitting with the legs flexed and abducted for the duration of a car ride presents any risk, whatsoever to children. If you are worried about your child’s legs in the car, make sure to take stretch breaks every 2-3 hours you’re in the car to help keep your child comfortable.

4-yr-old 40" RF in Momentum SceneraNEXTEmmaRF Marathon CT Ava rf Clek Fllo Addie RF ERF - Diono Radian R120 Anna 4EVER 2BritaxBoulevardG4.1RF bvct anna rf 1  GracoSize4Me70rf Rear-facing toddlers in TrueFit - reading book Rear-Facing 3 year old in NextFit RF in ETA Rear-facing First Years True Fit & Britax Marathon

See related article:

Mythbusting: My child’s legs will be injured in a crash if their feet are touching the back of the seat or if their legs are bent.

One Response

  1. ketchupqueen May 2, 2016