But it still has to come back out at some point, and reverse it's path doesn't it?
Yes it does, but you will get less contamination, although that may be academic.
It is similar to the "hood" on the glasses used for injectable liquids:
You have an elastic membrane and a sharp pointed object.
The pointy end pierces the membrane quite easily.
If it isn't sterile, it contaminates the contents.
Coming out, the membrane holds back.
It closes tightly around the needle.
This causes it to "drag" on it.
Ergo, less contamination.
Again, however, the difference may very well be entirely academic. I suspect that depends on what kind of cleaning you do up front, what kind of medical care you administer and how quickly you do so, along with (important) the size of the fissure. Unlike a fistula, where the tissue has died, you would be pushing through fresh tissue, which will attempt to close and heal afterwards. Given proper cleaning of the wound, sterile implements, and a fine enough gauge, it might be possible to deal with; a doctor should comment on that. I can only offer my conjecture.
All this is not to say I think it's a good idea, healthwise, regardless of the turn-on.
"If God saw what any of us did that night, he didn't seem to mind.
From then on I knew: God doesn't make the world this way.
We do." -- Rorschack, Watchmen.