I'm a right above knee amputee (RAK) as of September 11th 2007.
Here's a little bit of a story and hopefully some info you might like to read about.
One of the most important parts of a prosthetic limb is the socket (that's the bit that your stump or residual limb if you want to be more technical sits in) If the socket doesn't fit or is uncomfortable you could have a £50,000 knee,or other component for say an upper amputee and at the end of the day it would be useless as you couldn't wear or use the limb for very long. Imagine wearing a pair of really uncomfortable shoes for hours on end, ones that make your feet sore and get blisters. You can't wait to take them off and relax yeah!!!?, then imagine having to go through it all the next day and so on and so on and that will give you a small idea of what it's like to have to wear a prosthetic socket that is painful and uncomfortable.