Well, there could be various factors contributing to a re-replacement. These could be inherent issues like further degeneration, acquired ones like infections/ inflammations, issues with the implant or positioning etc. Without an evaluation it would be difficult to determine the reason in your case. It would be best to discuss the situation and the appropriate management in detail with your orthopedician.
Hope this helps.
I think you are referring to a Smith & Nephew. Did you have an injury?