At any rate, something worth noting is that whatever's going on here, it doesn't appear to be set during the near-future of MGS4, because that looks like a fairly old model of prosthetic (it's widely used today, but it hasn't changed much in a very long time). Could very well be about Big Boss/Naked Snake... sure he had two hands in later games, but is there any evidence that one wasn't a prosthetic? Those games were on the NES for crying out loud, you could claim almost anything about the characters' appearances and get away with it.
In addition to the jawline and mullet, that bandage covers the same eye that Big Boss is missing. So that's another piece of evidence that they're at least suggesting this is a Metal Gear game.
Lastly, I'd put good money on a bet that this entire trailer is for a single stage in the game... possibly a flashback or a side story, but the game itself won't stay in the hospital with a stumbling, wounded and largely helpless Snake/NotSnake. Remember MGS2?