Replacement hips, knees and other joints have a life expectancy, and while some folks sincerely believe the replacement will last forever, that has never been the case, or will it ever be. Human joints are incredible in that really tolerate a massive amount of abuse, yet continue to survive. They tolerate obesity, injuries, and viral infections and keep on plugging for decades.
Unfortunately, replacement joints are not nearly as high quality as the originals. They wear out, often in 5 years or less, depending upon how much usage they must endure. The more you use them, and the harder they are used, the faster they wear out - it's that simple.
The biggest problem with hip and knee replacements is obesity. The amount of excessive weight placed upon the replacement effects them dramatically. The best advice I have for anyone that is considering a replacement is to get down to your ideal weight. If for no other reason, this can stem off the replacement for years. It reduces joint pain of the affected joint and reduces wear by a huge amount.
In my case, it was my back, which has undergone surgery on two occasions, both of which were successful at the time, but in my case, the deterioration was caused by Lyme Disease, which went misdiagnosed by a lousy doctor for 18 months. He treated me for something I did not have, osteoarthritis, mainly giving me loads of aspirin, which only helped with the pain, but never addressed the disease itself. When it was finally, properly diagnosed it was too late and the spinal damage was already done. This, compounded by a couple injuries, forced my retirement at age 76. I am now hoping to get some relief from the pain by possibly undergoing a third surgical procedure, but not sure if this is possible. A neurosurgeon and orthopedic surgeon both told me that the damage is so severe that additional surgery could result in permanent paralysis from the waist down. Been there, done that - took five months to learn how to walk again - don't ever want to go through that again.
Now, if your normal activities are such that someone else does all the yard work, and most of the other physical things you used to do, that replacement joint could last much, much longer. However, for me, that would be a death sentence. I can't sit still for an hour, let along all day long like some of the retired folks I know. I gotta do something, even it it is wrong!
If I'm not out sailing the boat, mowing the lawn, working on rock gardens, etc..., I would go absolutely nuts (Carol says I'm already in that category, though.)
As Tony said, it is extremely important to go through the physical therapy programs post surgery. Now, some docs and hospital workers will try to con you into entering into an assisted living/physical therapy center, but that is not often the best route. More often than not, you will do much better by entering programs outside those settings, but you must have the will power to do this and not just sit down and expect that joint to get back to normal on its own - it's will not happen. The surgical procedure is brutal, a lot of muscle is damaged during the procedure. The damage can only be restored with intense exercise.
There is a lot to consider with this kind of procedure. Surgical techniques have improved over the years, but it is still a very traumatic proccedure.
Good luck,
Gary