prosthetic arm

i was wondering is it possible for one of my players to have a machanical arm and incorparate a sword or something into the arm so you can change from a hand to sword or is this not possible?

Are you the DM? You can just say "you have a mechanical arm, where you can swap from a hand to a sword". You probably don't even need to make it an item; just remember that there are advantages and disadvantages (can't drop the sword, can't use two hands).

If you're a player, you can ask your DM.