Knee-Surgery - explained in PalmerProject-Ski- and Snowboard-Lexicon

"Knee replacement, or knee arthroplasty, is a common operation done to relieve the pain and disability from degenerative arthritis, most commonly osteoarthritis, but other arthritides as well.[1] it consists of replacing the diseased and painful joint surfaces of the knee with metal and plastic components shaped to allow continued motion of the knee.

Incapacitating pain from arthritis of the knee affecting everyday activities -- particularly walking and standing -- is the main reason to have a total knee replacement. The patient must be aware of the risks of the surgery and be prepared to take those risks rather than continue with the symptoms."