I suppose that many of the posters opposing a Class 1 Medical for pilots with a prosthetic limb might review their position if a tram ran over their arm tomorrow.
I was astonished to learn that a Class 1 medical is available in this case but the CAA information linked in one of the first posts seems to be a sensible regulation.
Unrelated to acceptable risk discussions for commercial operations, one of the most succesful German aces flew a significant part of his career with one leg only (Hans-Ulrich Rudel). While this might not be a yardstick for commercial operations, it is IMHO evidence that pilots with prosthetics can have the "manual skills" required for the art of flight.