Biomechanics of Babywearing: Part 1 – Baby Positioning

Part one in a two-part guest series by Dr. Andrew Dodge, DC

How to wear your baby can be a confusing and, at times, very controversial subject. There are so many different carriers out there and just as many different positions in which to wear your baby. This post will focus on the biomechanics and development of your baby’s spine and hips and the most optimal carriers and positioning for both. It will also touch on physiological and neurological effects that certain positions have on baby’s development.

While inside the womb, baby is completely flexed in the fetal position. Its hips and knees are fully flexed and its spine is in a complete C-shaped curve. After baby is born, it takes several months for baby’s joints to loosen and their extensor postural muscles to gain strength. As baby grows and gains strength to hold their head up they develop the proper spinal neck curve. Also, as they begin to crawl, baby develops the proper spinal curves in the low back. These curves give the optimal structure for movement, weight-bearing activities, and proper neurological development.

When thinking about a position in which to carry your child, it is important to keep this development in mind. Putting your child in positions that challenge their stability too early or that can create too much or too little spinal curve may be detrimental to development. Abnormal or excess pressure in certain areas of the spine can create changes both structurally and neurologically.

Several studies have shown that excess low back curve, or hyperextension, can change the biomechanics of the bones and joints in the low back, creating instability (ie. Spondylolythesis) [i], [ii], [iii]. In children, instability in the low back can affect nerve supply and muscle control into the colon, bladder, and pelvic floor muscles. This can have an effect on the child’s ability to make, feel, and/or control bladder and bowel movements. Also, if there is an increase in curve in one part of the spine, there must be a change in curve or bone structure in other parts in order to compensate and create balance. This can contribute to the development of scoliosis [iv].

With changes in spinal curves, there will be altered movement, pressure, and tension in the spinal joints, muscles, and ligaments [v]. These changes will alter the neurological signaling from these areas of the spine to the brain, which alters overall brain growth, development and size [vi], predominantly affecting secondary motor programming pathways. This means that the pathways in the brain that control learning and executing movements will be abnormal and therefore the movements themselves will show abnormalities [vii].

Aside from the structural and neurological development of the spine you must also consider the development of baby’s hips. At birth, the hip joints are not fully developed. They are shallow ball and socket joints with very little stability. As baby grows and develops, the socket becomes deeper and more stable [viii]. With proper hip and leg position, the ball (head of the femur) will put pressure at the correct angle into the socket (Acetabulum). This is what changes the hip from a shallow joint at birth to a very deep and stable joint by the time your child is up and running around. If this joint does not form correctly and is left shallow, the ball has a greater chance of sliding out of the socket [ix]. When this happens it is called hip dysplasia. During this time of development there are more optimal positions that will allow for better hip growth. There are also positions that will increase the risk of hip dysplasia [x], [xi], [xii].

Keeping all of this in mind, lets talk carrying positions. Foremost, take precautions such as making sure not to block baby’s airway and always monitor them closely while they are being carried no matter how you decide to carry your baby. Next, when baby is brand new and still fully flexed with very little postural control, it is best to keep them in an all flexed and secure carry.

This is most commonly done using a sling or wrap with baby facing the wearer tummy-to-tummy. (Soft structured carriers may not give the same amount of head and neck support and are not recommended until baby is larger and more stable. This usually occurs by three or four months of age). To properly support the hips during these carries you can position baby one of two ways. The first is to frog-leg your baby in the wrap with weight centered on baby’s bottom. This keeps knees and hips bent without spreading the hips too far. The one thing to be cautious of is to not let any of baby’s weight be put on the feet when they are frog-legged. The second way to carry baby is to have baby’s knees open just as wide as the pelvis with ankles in line with the knees and feet out.

This second option has been a confusing recommendation made by the Babywearing Institute, as it is often mis-interpreted. However, this legs spread/feet out recommendation is different than the way that you would carry an older child (explained below). Instead of extending baby’s legs and wrapping them around you, baby’s legs are completely flexed and only open as wide as the pelvis. With the wrap cradling baby from just behind the knees and around their bum and back, the feet are “out” of the wrap.

As baby grows they develop more stability and can more naturally open their hips. This allows them hold on to the wearer with their legs. At this point the most optimal position for spinal and hip development is with baby sitting back in the carrier in a knees up squatting position. This position is easily achieved in a front (tummy-to-tummy), side, and back carry. With so many options to wear baby in the most optimal position and so many carriers in which to do this, it really comes down to personal preference in how you choose to wear your baby.

There are a few positions that have become more controversial and dividing among babywearers. The first carry is a tummy-to-tummy position with a narrow seat for baby. These baby carriers are not recommended for several reasons. The first is that this type of carrier allows baby’s hips to angle downward, causing their knees to be below their hips. This does not allow the hip joint to be aligned at the proper angle and allow for optimal development of the hip joints. This can predispose your child to developing hip dysplasia [xiii]. While not all children who are worn in such a way develop hip dysplasia, this is something that can contribute towards that process. This carry also puts all of baby’s weight directly on their pubic bone.

It is very similar to you sitting on a bicycle seat with your legs hanging off the sides and riding down a bumpy road. It may not be as uncomfortable for baby because they do have a little more padding with a diaper and less sensation than we do in that region, but over time it will become very uncomfortable, and it will change to stability, alignment, and bone formation and development of the pubic bone and hips. Finally, with all of baby’s weight put on their pubic bone and their legs hanging at a downward angle, baby’s lower spine will be forced into hyperextension. This, as I explained above, is less than ideal.

The second controversial position is that of the front-facing carriers. This position is also not recommended for several reasons. Most commonly this type of carry is not looked fondly upon because of the biomechanical implications. It is extremely difficult and quite uncomfortable for the wearer to get baby into the optimal knees up squatting position. This leads to most front-facing babies either with legs dangling and/or leaning forward, creating hyperextension of the low back curve. If the wearer can get baby into a good position with baby’s knees above their pelvis, this may allow the low back to be in a good position. However, with baby’s back against your torso, this will create flattening of the mid-back curve, put extra pressure on baby’s ribs, and change stability and curve in baby’s neck. In reality this may be a better choice if you decide that you are going to wear you baby front facing, but optimally, there is really no good position for your baby front facing. (High back carries and hip carries can put baby in a great position and let them see more of the world, if they are constantly fighting to see more – like my little guy!). Despite this being the most common argument against front facing carriers, there are other things to consider before you wear your baby front facing as well. Neurologically, it is great stimulation for baby to be able to see the world around them and experience different environments; however, baby has no way of hiding or “escaping” from the stimulation when he is facing away from you. This can have negative affects on a child’s emotional and neurological development [xiv]. You may also not be able to see signs of distress or over-stimulation when baby is facing away from you. When baby is being carried on your back or your hip you will either notice different signals baby is trying to send to you, or you will see that baby can easily retreat back into you when the stimulation becomes too much. In addition to the biomechanical and neurological benefits to wearing your baby tummy-to-tummy, there are many physiological reasons to do so as well, especially with newborns. When positioned tummy-to-tummy, baby needs less oxygen and is able to conserve energy better, can digest food better, and can more easily regulate their own body temperature [xv]. (As mentioned in my previous post).

All in all there are a lot of choices on how and why to wear your child. Each person must do what they feel is best for them and their baby. I have said this time and time again to my patients: “The choices that you make are yours. I only want you to be informed and know why you are making the choices that you make. No matter what choice you make just be informed.”

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References:

[i] Isabelle Villemure and Ian A.F. Stokes, “Growth Plate Mechanics and Mechanobiology. A Survey of Present Understanding,” Journal of Biomechanics 42 (August 2009): 1793-1803.

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Dr. Andrew recently moved from Fort Worth, Texas, with his wife Nicole and their 11-month-old son Luke, to the beautiful Shenandoah Valley of Virginia, where their children will be able to grow up around extended family. He is a chiropractor, and practiced in a family clinic in Forth Worth prior to his move, treating mostly expectant mothers and children. He is currently in the process of opening his own clinic in Virginia. In addition to his doctor of chiropractic degree, he is also in the process of certifying for a diplomate in neurology as well as an advanced certification in pediatric care. Dr. Andrew and Nicole are enthusiastic babywearing advocates and have established the Shenandoah Valley’s first babywearing library.