When someone experiences a vertebral rupture due to an accident, they often lose general movement in specific parts of their body. However, I’ve always wondered why, given the advancements in technology, it remains challenging to rebuild the vertebrae and allow the body to heal itself, given the body even has the ability to do it.
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It’s not the broken bone that causes mobility loss, it’s the damaged nerves inside it. They can’t be repaired with current technology.
I’m on the cell biology side and not the material sciences/bioengineering side so. With this I am hypothesizing/extrapolating somewhat. But:
While the body does have some pretty good healing properties, it’s frequently not true regeneration. Actual regeneration is not present in a lot of cell types. Your body can heal and replace some cells with ease, especially when those cells are *designed* to be replicable, such as outer layers of your skin and the lining of your gut. Other cell types, don’t recover so well. Healing is more about patching and covering wounds up to keep you alive and as healthy as it can manage, maybe with something completely different than what used to be there before (like scar tissue).
Legitimately, the “what doesn’t kill you makes you stronger” is actually very inaccurate in a lot of biology–your body accumulates damage over time, that does not heal to its previous state, and aging is potentially owed to some of this accumulated damage just due to living. And, some cells do not tolerate damage well. Nerve cells are delicate, frequently very long lived, and don’t really have much of a good replacement system when they’re lost. In some organs, damage can be made up for by other cells taking the jobs of the cells that were lost. Maybe, at some % lost total capacity, but that’s rarely something you notice unless it gets bad. Basically post-development is usually the best any particular part of your body will be, as the process that generated them is the most whole and complete way of getting everything in the right place and made of the right stuff. Everything after that is patching it together as best you can, for the many parts you aren’t equipped to replace outright.
Joints, suck. Patchwork healing can screw them up, little deviations or imperfections can cause huge problems, and there’s no way to just start over from scratch. We do have advanced materials, but making sure that agrees well with the body is a huge challenge, especially if they could be recognized as foreign and get patched over as a potential hazard, fought by the body they are inside of, or wear down in a way the body isn’t prepared to deal with for its natural what-should-be-there-instead. Or it just, doesn’t go together well.
And if there’s nerve damage and the like, there’s not an existing technology to really replace that yet, even if you restore the joint well.
The vertebrae protect the spinal cord, part of the central nervous system. Unfortunately rebuilding a vertebrae would not solve the issue of restoring sensation and voluntary functionality of the extremities. That task requires the knowledge and skills necessary to repair or rebuild artificial spinal cords that are compatible with the innate structures of the human central nervous system.
The parts of the nerves that need repairing are too small to manipulate physically. Our best microsurgery isn’t good enough to repair that kind of damage yet. [We’re getting there; it’s an area of active research.](https://pubmed.ncbi.nlm.nih.gov/17478254)
The chemistry is too complex for a chemical repair solution (drugs). Most medications target very specific parts or processes of a cell; nerve repair involves the entire cell, chemistry that is many orders of magnitude more complex than any medication can handle. We have made some progress in using chemistry to trigger self-repair, but nerves’ self-repair function is mostly non-existent. Stem cells appear very promising in this direction, but stem cell research is mired in religious controversy, so progress is slow.
Repairing bones is fairly easy. It’s done all the time, abd bones are happy to regrow.
But we’re not made out of one solid bone, we also have joints, and those joints, including the disks between vertebrae, are difficult to repair because the soft tissues that make them up do not regrow as easily as bones themselves. That’s why stuff like a torn ACL, achilles tendon or carpal tunnel basically are life-long issues.
Of course, that ignores the fact that the spine has the spinal cord. And that isn’t difficult to repair. It just isn’t possible. We can’t repair nerves. There’s ways to somewhat encourage a degree of natural recovery where possible (like if the spine wasn’t totally severed, just mostly), but it’s always a minor improvement. Maybe return some feeling in a paralysed limb, but not movement.
Vertebra aren’t just cement spacers, they are very complicated, dynamic structures so impossible to fully reproduce. Any prosthesis is a poor substitute.
We can — while the more common treatment is to fuse vertebrae on either side of the ruptured disc, there are artificial discs that can be implanted, too.
There are limitations on them and their use… I had 2 ruptured discs but couldn’t have the artificial discs because they were non-consecutive vertebrae and insurance dubbed it “experimental” due to lack of data. Had it been one disc or two consecutive ones I’d have been able to get them. As it is, with the 2 fusions at C3-4 and C6-7, I lost about 5% range of motion in neck.
The simplest answer I received for this question was that nerves heal very slow and essentially they develop scar tissue faster than they can heal.
I know It’s not 100% correct but maybe good enough for ELI5 ?
We can! The problem most of the time is the nerves inside the bones rather than the bones themselves. Not only are nerves hard to repair but the ones in the spine are so important that any damage done is almost guaranteed to leave you with some type of problem no matter how much repair is done.
Imagine a electric cord. But instead of 1 giant cable that is solid all the way thru, it has millions of tiny tiny cables. All bound together. To make the cable.
A single cut cable? No problem. We can fix that. We find both ends and connect them. Cut them all? Well it’s fine we can connect them together again but we have no idea where each cables goes. Maybe we connect them wrong and trying to move your legs ends up moves your left butt instead.
Beyond that we don’t acutally have the knowledge to do fix it to begin with
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