My father developed a problem in his wrist after he injured it a few years ago. His wrist began to bend forward and now he can't straighten it out. His doctor is talking about using some sort of splint that he has to fix every day to help stretch his hand out. Wouldn't surgery do the trick?
It sounds like your father has wrist stiffness, which is making it impossible for him to use his hand and wrist properly. Usually, this is first treated with physiotherapy, so if he has not yet tried that, you may want to mention this to his doctor. If physiotherapy doesn't work for stiff wrists, patients do sometimes have surgery, but others use a special splint that stretches the wrist, called static progressive stretching.
To do this, your father would have to put on a special brace, once a day in the beginning, and adjust the angle on the brace so the wrist is stretched, but doesn't hurt. That position is held for five minutes. Then, if it's not painful, he increases the angle a bit and holds that position, and so on, for a set amount of time. After a few days, these sessions increase in number. This treatment seems to be quite successful in many cases.
Surgery can be done, but surgery always has risks, from infection to the surgery not clearing up the problem, so it's always best to see if there are other ways to help before operating.