how does a cut finger get resewn back on with full functionality?
In: Biology
Hand surgeon here. A cut off finger that gets reattached doesn’t get full functionality back unless it is a fairly young child.
Surgically it is complex and a single finger will take hours to attach, then multiply that with however many fingers you’ve put through the table saw. First step is to stabilise the bone, this is usually done with two crossed, smooth steel wires that are drilled in to the bone. Once that bone is stable you tend to suture the tendon(s) back together. At the base of the finger you have two, after the first joint there is only one. At this point you get the operating microscope with 25x magnification in and suture one of the two arteries and the nerves of you can get them to match up. If there is a bit of artery missing you can borrow one of the veins on the inside of your wrist to plumb in as an extension. For the nerves you either sacrifice one or use a synthetic nerve tube to guide the growth back. Finally you flip the hand over and suture the tendon and two or three veins. With any luck it works.
The results aren’t great though. You will have a permanently stiff finger with poor if any sensation and it will be very cold sensitive. This is why in many countries you don’t reattach a single finger unless some specific cases like in children since they have much better results or if it involves a thumb. The US is different and I suspect much of it comes down to remuneration.
A finger cut off at the middle will do pretty well but the higher you go the worse the results will be. Once the major nerves to the muscles in the hand or even worse arm are severed outcomes are poor. The best you could hope for with a reattached hand would be 50% of the grip strength and enough sensation that you can feel if you stab yourself with a needle.
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