I'm constantly amazed by the advances of medicine. One problem with getting a knee replacment is that there's a one-size fits all (or one of only a few selections fits all) system, that doesn't always work well for people of different shapes and sizes. Knees wear and tear differently because of different body types. But new technology is taking away this issue. Check out this article: 

"A total knee replacement can take place using Shapematch technology. MRI images are used to create a 3-D image of your knee. Then a custom fit knee is made and precisely placed." 

Now instead of having to adjust your life around a knee that may or may not quite fit, the knee is made to fit your life and your body. 

Only about a dozen surgeons in the US are currently using this techonology, but I'm sure that it's going to be standard practice before long.