many thanks, what is the chance the fix will dislocate?

My family was told there are patients who discloated the fix, and had to go through the surgery again to put it back in. When the thing dislocates, they said it is very painful. Second surgery will cost him even more.

The biggest concern my family has is my dad may walk around without his knowledge. This could make the fix dislocate easily. He has Parkinson, which will make the dislocate easier. 

I wonder if my dad will be very weak, and had to lay in bed after surgery. If we give him some medicine for his 狂想， or老年痴呆， he may stay quite during night. Right now, he only has symptom at evening time, not day time. 

Will you give me some suggestion on my family's concern? The hospital agrees to the surgery, but now my mom and other family memebers hesitated. The surgery will be on Jan 3