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The Growing Child: How Does That Work?
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Posted on: 03/24/2011
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Many's the time a parent has told a child complaining of leg pain that they are having "growing pains" and it will pass. No one has a better explanation for this. Even the bone scientists agree there may be some truth to the idea. New discoveries in the last 10 years about how bones grow might eventually shed some light on this subject.
To help us understand bone growth in children, the authors of this article review the anatomy and physiology of the physis (growth plate). By understanding how growth factors and regulatory factors control physeal expansion, it may be possible to deal with physeal abnormalities, growing pains, deformities, and injuries.
The physis is a complex structure with many different types of cells (bone, cartilage, collagen) and multiple layers. There is a network of tiny blood vessels called capillaries to supply the area with nutrients and oxygen.
The physis is unique because it must be flexible enough to grow (i.e., it has not yet hardened into bone). But it must also be strong enough to withstand tension, compression, and shear loads placed on it during the many and varied activities of children.
Growth is regulated by hormones, feedback loops, and factors that signal when to increase or decrease cell growth and when to stop growth altogether. In order to turn collagen into bone, there has to be just the right amount of calcium, alkaline phosphatase, and matric metalloproteinase.
There are actually tiny packets called vesicles inside the chondrocytes (cartilage cells) that contain these chemicals. By some mechanism at the cellular level, these vesicles open up and release their contents at just the right moment for mineralization of the bone.
Anything that disrupts even one of these pathways can lead to abnormal physis. Lead poisoning, metabolic bone disease, tumors, infection, and trauma head the list of reasons why bone growth can get stunted or altered. The focus of this article is on the results of physeal trauma (most often from bone fractures that go into the growth plate).
Disturbance of the growth plate resulting in stopping bone growth can lead to a limb length difference (arm or leg) from one side to the other. Studies show that up to one-third of all bone fractures in children that extend into the physis result in this type of growth disturbance.
The factors that determine growth problems after fracture include the location of the injury, whether or not the blood vessels to the physis were damaged, and how close the child was to skeletal maturity (end of bone growth) at the time of the fracture.
One of the big dangers of physeal injury is the formation of a physeal bar. In the process of healing, bone is laid down across the break in the physis. A bar of bone is created that essentially stops any further growth of the physis on one side. The other side continues to grow causing angular deformities and uneven bone growth.
Scientists don't know a lot about physeal bar formation. They have been able to show that if only a small part of the physis is damaged, then bar formation does not occur. Until it is known the exact mechanism by which this bar forms, we are powerless to stop it from happening. Research is actively seeking ways to unlock the mysteries of this problem.
That brings us to the next topic: treatment for physeal bars once they form. The bar can be removed surgically. The surgeon must put a piece of graft tissue (often fat harvested from some other part of the body) in the space created by cutting the bar out. Without this interposition tissue, the bone will just grow right back again.
Animal studies are being done to find ways to stop physeal bar formation. Until that happens, research is also looking into finding better ways to support the physis after bar resection.
For example, efforts are underway to find a chemical bonding that will give stability without impairing growth. If the entire growth plate has to be removed, it may eventually be possible to use gene therapy to regrow normal physes. This is only one example of what's referred to as tissue engineering.
In summary, normal growth of the physis (growth plate at the end of bones) is a complex process that is only partially understood. Growing pains without injury will eventually go away. But damage to the growth plate from bone fractures (and other nontraumatic events such as tumors or infection) creates a whole different set of problems. Problems that we don't have an easy solution for just yet.
Ongoing efforts of scientists in the area of genetic and tissue engineering are approaching the problem from one direction. Scientists studying the cellular processes involved in the formation of bone may also have some success. They hope to crack open the mystery and find the key to preventing physeal bar formation. Then it would be possible restore normal bone growth and repair.
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References:
Pooya Hosseinzadeh and Todd Milbrandt, MD. Histology of Physeal Injuries. In Current Orthopaedic Practice. March/April 2011. Vol. 22. No. 2. pp. 130-134.
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*Disclaimer:*The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic. |
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