I was doing more reading recently and I thought more about how the bones keep their thickness in tact with a relatively constant thickness. Obviously besides increasing in length, the bones are also constantly changing in the radial direction, which is termed appositional growth. To keep the bone width about the same the rate of bone absorption by the osteoclasts and the rate of bone creation by the osteoblast must be equal.

Here is a theory that I am proposing although I haven’t been able to get to a medical textbook to confirm this yet. My guess is that if we can figure out the direction in the radial direction on how bone is created and resorbed, we can simulate cartilage regrowth in the same direction to recreate a new growth plate by the natural process through either a stem cell implant or a chondrocyte/hyaline cartilage implant.

The osteoclasts seem to be working closer on the inside of the long bone, in the trabecular inner region breaking apart the nonliving calcium crystal deposits and the lacunae pits. The osteoblasts on the other hand creating the osteoid and forming new layer of bone seems to be occuring just underneath the layer known as the periosteum. from this process, if we think about the direction of bone growth, from creation to destruction, we can see that the direction of bone growth is inward. As the older bones gets replaced by the newer bone, but still keeping the constant distance in thickness, that should mean that the inner bone cells gets pushed closer and closer to the middle where they eventually get to the osteoclasts which dissolve the bone cartilage formed around there.

My suggestion then is that if we might be able to do a far less invasive surgical procedure where we just attach or plug the layer just beneath the periosteum with mutiple cartilage implants in a way to surround the bone to form a donut shape. If the direction of bone growth is in the radial direction going from outside in, then theoretically the attached cartilage would then be able to fuse into the cortical bone and slowly completely surround the entire bone and develop into a new growth plate. We know that the entire body get’s all of its cell replaced every 7 years, or so goes the urban medical myth. I don’t know what is the turnover rate or average life expectancy time of the bone cells going from the outer layer to the inner layer but if it is less than 1 year, we should be able to possibly get the entire bone area to absorb cartilage for regorwth layer.

However, the cartilage design will have to be at least 5 layers. There must be the initial sacrifice layer which the bones will eventually ossify once the cartilage gets embedded into the cortical bone over time. There must also be a layer of perichondrium on the other side of the cartilage which will eventually be used to encapsulate and protect the third layer from beign penetrated by blood vessels. It seesms that vascularization of the cartilage in the growth plate seems to result in the ossification process. The perichondrium which was around seems to be able to keep the blood vessel out, at least for a certain amount of time. Finally, at the middle of the cartilage implant will be the actual growth plate cartilage with the right chondorcytes, collagen, and proteoglycan inside.

Imagine in your mind the picture of a Macdonald’s Big Mac and you have an idea of what I am talking about. The outer bread loafs represent the cartilage which will get ossified in the gradual embedding process. The meat patties represent the perichondrium which will be to protect the middle layer and give the middle layer it’s growing abilities, and the middle patty represents the real cartilage which will eventually become what will be our new growth plates. The design of the implant must also take into consideration the constant ossification rate of the initial cartilage so the implants can’t have constant thickness themselves, but move from the intial contact to be thicker than the later thickness of the implant.

Now this is where I would like the readers (you guys) to finally give your professional opinion on this idea. I am almost positive the direction of appositional or radial bone growth goes from outside inwards. So we can possibly allow for a this process to push the implant slowly inward into the bone, until one entire thick region of the original metaphysis area gets replaced completely by cartilage.