Scotty suffered damage to his fingers on D-Day. He was always self conscious about it and managed to hide that hand in most episodes.
Me, I would have considered it a badge of honor.
From what I’ve read there is only 1 shot where you can see his lost fingers. I believe it was in “The Trouble with Tribbles” when he walks in with an armful and says “aye, they’re in the machinery all right”.
He lost one, actually. On at least one occasion, you could spot it.