What is this Orthopedic overnight case?

My grandpa has had his hip replaced in yesteryear, but today what they thought was a trapped nerve is actually a skin where he needs his hip replaced again. What is this case call? I know what happens in the hip replacement surgery, so has the metal become rusted?
Answers:
No, the metal didn't rust. Likely he had the ball replaced and the socket now also desires replacing, or some other such structural problem. The hardware is all but indestructible, so lacking specific knowledge, bet on the bones.
Exactly as Dr. de Witt pointed out, it's far more feasible either loosening of the joint or an actual infection. This can be a very difficult problem for the orthopedic surgeon to sort out even near advance nuclear and MR imaging.

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