Copy/pasting my reply from further down.

>This is called a fasciotomy. It's to prevent compartment syndrome.
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>For an ELI5; When you injure something, your body responds naturally by inflaming the area. In other words, swelling up the area. Your body doesn't care about side effects and doesn't monitor what this can cause in the process, it just wants to deal with the current injury. When your body goes too hard with this, or swells too much, it increases the pressure under the skin or muscle. If this pressure gets too high, it can squeeze the arteries and veins inside the muscles too.
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>When these arteries get squeezed, it can cut off blood supply completely, to anything past that area. Within minutes of complete loss of circulation, irreparable damage to everything past the bloodflow blockage, can occur. It can lead to losing a limb or even killing you (blood will clot, then when swelling goes down, the clot can move to your heart or brain and you die.
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>To prevent these complications, there is a procedure called a fasciotomy. This is basically just a fancy word for cutting open a hole so that some of the pressure has a place to go. Think about a stress ball. When you squeeze it really hard, you're putting pressure on it, and the stress ball will move around to disperse the pressure youre squeezing. Your body cannot do that, if you squeeze your arm as hard as you can, it doesn't act like a stress ball and just move somewhere else, its stuck there.
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>So this fasciotomy, opens up a hole for the tissue to squeeze out, just a little bit. Now, it wont completely come out cus again its tissue, its muscle, its all attached, but it gives it a place to kind of move around a little bit. This little bit of pressure release is typically all that is needed to relieve pressure on the arteries and veins, allowing bloodflow through again, saving the arm/leg/whatever.
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>Typically this is a last resort emergency measure.
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>hope this helps