sollers

It certainly used to be so (I don't know what the current position is), and to be fair before decent prostheses it would have been pretty difficult to celebrate the Mass one handed. But you can't unordain someone (even defrocking/ laicising doesn't actually cancel the ordination, it just means you can't perform priestly functions), so a one-handed priest would still be a priest, even if he might have to take early retirement.