How do you tell if your artificial knee is wearing out?

Get checked. If you are concerned about your artifical joint, see the surgeon who placed it and get his/her opinion. You can even get a 2nd opinion or 3rd if necessary. Usually you will have laxity, perhaps pain, and perhaps loss of previous function. A feeling of unstable-ness of the knee may be present. Is there swelling, reddness, pain, fever? By all means, be seen.
Artificial knee . You should get it routinely checked by your surgeon to look for early signs of wear or failure.