From an article on the interenet: "Joint Replacement Try to delay replacing a knee or hip joint as long as possible. An artificial joint has no local immunity, so if you get an infection anywhere in your body, you are at increased risk for that infection ending up in the replaced joint. A general rule is to put off replacing a joint until it hurts so much that you cannot sleep at night. An artificial joint is held in place by a spike that is driven into the middle of a long bone. This markedly weakens that bone. If you fall with a replaced joint, you are at high risk for cracking the bone around the spike of the joint replacement. The broken bone around the spike may never heal so that you lose the ability to exercise that joint forever. If you have a joint replacement, you should restrict running and jumping and exercises that put you at high risk for falling. Choose exercises that use smooth motions such as elliptical machines, cycling or swimming." This article was originally published on www.drmirkin.com. Subscribe to their free weekly Fitness & Health newsletter.