United Brachial Plexus Network, Inc.

I just recently found this forum. I have been using the search feature trying to learn about doctors and treatments.

I am sure there are people like me reading and trying to learn. We have an adopted daughter with BPI. I mention that she is adopted because we don't have medical information about the injury. She was 26 months old when we got her.

Today I read an old post by Claudia and I just thought it was really eye opening for me. She said "This is a very complex and individual injury. Even two children with the same nerves injured will not have the same "disabilities"." That is really helping understand the varied information out there.

I just thought I would share as maybe there is another newbie like me that could benefit from that info.

Cindy

Cindy,

That is definitely true in the case of permanent nerve injury, but we need to be careful because there are a range of BPIs (the milder ones) which do follow a very consistent and predictable pattern of full or nearly full recovery. We don't see too many of those on this site, but they still make up the majority of injuries and I would hate it for parents of newborns to think there was absolutely no hope of a good recovery.

Here's my best attempt at explaining the different types of injuries and why the milder ones are fairly "predictable" while the more severe ones are not.

Basically, the individual nerves (axons) are surrounded by a thin "coating" (myelin) and then enclosed in another "sheath" (endoneurium). Bundles of these sheathed nerves are then enclosed in bigger "tube" (perineurium). Bundles of these tubes are contained within even bigger sheaths (epineurium). These form the nerve trunks that insert into the spinal cord between the vertebra. The permanency of injury, as well as the complexity of the resulting disability, depends on which of these components is damaged.

Generally speaking, the nerve bundles are damaged from the "inside out" - meaning that the nerve cells break first, then their sheaths, then the smaller enclosing tubes, then the outer sheathes, with increasing stretch.

The mildest injury (Neuropraxia) just creates some swelling that impinges the nerve bundles temporarily and everything fully recovers within a couple of days with no permanent injury. If the nerve cells (axons) themselves, or their coatings (myelin) are injured (Axonotmesis), but their containing sheaths (endoneurium) are intact, the nerves can and will regenerate and end up back at their original "targets" with nearly complete function. Nerve cells regrow at 1mm/day and so is complete in an infant by 1-2 months time. It takes a little longer for the nerve coating (myelin) to fully reform so function will continue to "improve" for up to a year.

With even greater stretch, the sheath containing the nerves can be damaged (Neurotmesis). This is the level of injury where it starts to get very complicated and individual. That is because when the nerve sheathes (endoneurium) are damaged, the nerves are no longer individually "contained" so that, when they regrow, they can end up regrowing down a different pathway than they originally occupied. If the larger tubes (perineurium) is damaged, and then the "mixing up" can be even greater. And if the enclosing sheath (epineurium) is damaged, there is even the potential that the nerves will regrow outside the original nerve bundles completely and form masses of misguided nerve tissue called neuromas. The worst injuries are when the entire nerve bundle is pulled out of the spinal cord (Avulsion).

Recovery completely depends on how many nerve cells (axons) make it back to their original locations versus how much "intermingling" and "loss" there is during regeneration. Any injury involving injury to the actual nerve cells (axons) results in the nerve cell dying and regenerating back from above (closer to the spinal cord) the site of injury. With the first two levels of injury, the nerve cells are either not permanently injured, or the regenerating nerve cells are still "guided" back to their original targets by intact structures. And so recovery is swift (within 1-2 months) and complete.

But once those enclosing structures are damaged, recovery becomes extremely individual. Since the nerves are no longer individually guided during regeneration, a nerve cell that originally went to the biceps, for instance, can end up going to the deltoid or the triceps instead. Some of this "mix up" can be resolved in the brain, which has a remarkable ability to "reprogram" itself and control the nerves even though many end up going to different places after recovery. This is why most children continue to improve after muscles initially become innervated. The brain is able to "figure out" out an amazing amount of the chaos that results from the regenerating nerves. But certainly not all, and it completely depends on how complicated the resulting nerve picture is. If the outer nerve sheathing is disturbed, some nerve cells may basically regenerate outside the nerve bundle completely and be "lost", and these cannot be compensated for in the brain.

If all the structures are completely severed and separated there will not be any recovery without the structures being reconnected via surgery, so that the nerve cells can regenerate. This usually requires a graft as generally an entire area of the nerve bundle must be replaced. Since even the best surgery cannot reconnect each individual nerve cell sheath (endoneurium) - and frequently the surgeon has to make educated guesses as to what went where within each bundle - there is still considerable "mixing up" of the nerves as they regenerate down the surgically repaired pathways and you get the same very variable recovery. Some kids actually do remarkably well... probably because their regenerated nerves ended up pretty "organized" and their brains are able to "figure it all out" after primary surgery. Most do not experience full recovery.

If the entire nerve bundle is pulled out, there will be no recovery unless the sheathed nerve trunk is reconnected to another "source" of growing nerve fibers. Research is ongoing in this area, but generally speaking once the nerve cells are severed at the level of the spinal cord, they will not regenerate. When we speak of "avulsed C8 being grafted to C5" for instance, what we mean is that the nerve conduit bundle C8 is grafted to a portion of C5 which is still connnected to the spinal cord. The original nerve cells which came out at the C5 level are lost completelthey will not regrow. The avulsed C8 bundle then consists of a bunch of bundled, sheathed nerve conduits but no live nerve cells until it is reconnected to another source for nerve cells. Once reconnected, the new nerve cells will grow down the C8 pathways and hopefully arrive at the target muscles. The "plasticity" of the brain allows the brain to essentially reprogram these nerve cells for different purposes, to a greater or lesser degree also mainly determined by chance.

Sorry for the huge long discussion. Basically, what I'm trying to say is that mild injuries ARE pretty similar and very predictable, in terms of timelines for recovery and potential for full recovery. The variability with more severe injuries, both in terms of time to recovery as well as amount of recovery, is because different structures become damaged with greater stretch.

Kate

Kate
Thanks for taking the time to post all this information.
I am sure it will help those of us without medical background to understand this complicated injury better.

Kath robpi/adult