When a person receives a limb donation, how do surgeons “wire up” the nerves so that the recipient can use the limb and feel sensation from it?
In: Biology
Here is a short youtube video about a hand transplant procedure
[YT-Hand Transplant](https://www.youtube.com/watch?v=d5bwRhHdgCU)
From what i know after removing dead tissues and recconecting everything people start to feel and sometimes even move the new limb.
(Edit: I’m hoping to create a discussion blog, where we can discuss biology/medical related topics + read about interesting findings.)
Quick answer:
Recipient’s and new limb’s nerve fibers are connected => Recipient’s nerve fibre grows along the new limb’s nerve fibre and stimulate the surrounding muscles, making it functional (able to feel & move) => it takes months until the recipient’s nerve fibers have fully grown into the donated limb, making the whole new limb functional.
Long answer:
Limb transplant is a very complicated process and takes hours to finish the surgery. For a limb transplant to be able to regenerate function and sensation, the recipient must first have the nerves for the limb (literally), meaning the limb to be replaced was broken due to an accident or a disease. People who are born without that limb usually cannot perform this limb transplant, as they do not have the correct nerves.
The transplant surgery consists of 3 steps:
1) Fixating bones
2) Reattaching arteries & veins
3) Repairing tendons and nerves.
The third step is the answer to your question:
The nerves of the new limb will be surgically connected to the body’s nerve fiber. That’s when nerve regeneration and the healing process begins.
Healing process: After connecting the old and new nerve together, the recipient likely isn’t able to move right away. The recipient’s nerve fibre will take the new nerve as a template, the fibre grows outwards from their body into the donated limb. Until complete regeneration of nerve signals in the new limb, it can take months. That’s also one of the reasons recipients have to go to therapy to practice care for their new limb.
A bit off topic, but one of the most controversial body transplant-plan has been head transplant. But this is a whole new discussion.
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Welcome back for updates on frequently asked questions
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Edit:
1) How to surgically connect nerves?
“The surgical nerve repair will be done by stitches.
A nerve, in simple terms, is composed of the axon/nerve fiber (which transports nerve signals) and the myelin sheath (which protects the axon).
When reconnecting nerves it’s only possible to stitch the sheaths together and not the nerve fibers itself. However, stitching the sheaths together creates a pathway for the new nerve bundle/fibers to grow along.”
Answer from u/surprisestupidity in the comments: “Nerve bundles are composed of many neurons surrounded by myelin sheaths with various layers of connective tissue sheaths. Think of it like how a bundle of individual wires can be wrapped together to form a thick a thick cable. It is actually the connective tissue sheath(the wrapping) around a BUNCH of neurons that are stitched together. The individual neurons are still disconnected within the stitched sheath but ideally, over time, each recipient neuron connects with the ends of donor neurons in the transplanted limb.”
Answer from u/IceEngine21 in the comments: “Plastic Surgeon here: You can also use nerve tubes when there is a small gap between two nerve ends, as a sort of bridge and guidewire.”
2) How to stitch nerves together when they are so small?
“The process is called microsurgery.
The art is mastered by few top surgeon experts in the world, through the use of microscopes and special techniques.”
3) Why can’t we regrow the spinal cord?
“There are 2 nervous systems: the CNS (central nervous system) and the PNS (peripheral nervous system). A damage to the CNS is irreversible in most cases due to various factors, whereas if to the PNS the regeneration rate is around 30%. A limb transplant affects the PNS, therefore nerves can regenerate. However, a spinal cord injury affects the CNS where nerve fibers almost definitely won’t be able to regenerate. However, there have been many ground-breaking studies on this topic, making spinal cord injuries seem less impossible than before.”
4) How well does the limb work?
“Whether or not the patient can regain complete control is complex. Assuming the new limb isn’t rejected by immunity, the patient will need months to retrain their new limb. If the nerves regenerate successfully + adequate physical therapy, it’s possible for the new limb to function very well though, complex movements such as tying shoelaces would be possible too!”
5) How come the body doesn’t reject the new limb?
“1. Find a compatible donor: matching blood type, limb size, medical conditions.
2. Immunosuppressants after the transplant.”
6) Is it possible to regrow the optic nerve?
“The eye’s optic nerve is much much more complicated than other limbs’ nerves. For once, they are tiny and packed tightly together, each photoreceptors (rods and cones) have their own nerves to detect colours and brightness. And when there are about 125 million photoreceptors in a few mm space, that can get quite difficult, not to mention the optic nerve is more complex than just a bunch of nerve fibers:)”
7) How does neuron regeneration feel?
“A good explanation is:
When you have been sitting on your leg for a long time and stand up, your leg feels numb, unpleasant, tingling. This is how neuron regeneration can feel like around the time. The tingling feeling in one area means new nerve endings are formed there.
Pain would be a sign of irritation.”
8) Have head/body transplant ever been done?
“Head transplant have been done on cadavers and some animals successfully, even though they had to die shortly after that new transplant due to ethical issues.
It’s never been done on live human, but the Italian Dr. Canavero has worked on this goal for a very long time. A head transplant directed by him almost happened last year, but the patient decided to not commit to the transplant anymore”
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Thank you for reading.
This is from massgeneral.org
Surgical nerve repair involves exploration of the injured nerve and removal of injured tissue or scar from the nerve endings. After that, a nerve can be directly reconnected if there is enough length on the ends to allow for a good quality repair without tension.
Another website says after healing begins the nerves regrow and “reach out” to stimulate the surrounding tissue allowing for reattached limbs to work.
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