Sounds like angel wing to me. You can try to fix it if they are still young enough.
Take the wing tips, turn them back to the way they are supposed to be, tuck them up under the main wing bone and tape it together. Usually by the time the tap comes off they are fixed, they really don't like it as they cannot spread their wings and being a goose you might have to reapply because they like to pull on things and might undo the tape.
I have only done 2 muscovy ducklings in the past and 1 fixed the other I think I left too long so didn't work.
I have a gosling to do right now maybe I can get some pictures of the process for you.
I know there was a site that showed it, but I am not at my computer right now so will find the link when I can.