When all the cartilage in your knee is gone, the only effective treatment is to replace the whole knee. Knee replacements are now lasting for twelve to twenty years or more, and most remain pain-free. The ends of bones are soft, so they must be covered with a thick white gristle called cartilage. Once damaged, cartilage can never heal. An affected person spends the rest of his life losing cartilage until the cartilage is completely gone and the knee hurts 24 hours a day.
The only effective treatment at that time is to replace the entire knee. However, the artificial knee can become dislodged from the bones and may need to be replaced after several years. The area will be so full of scar tissue that a second surgery is far more difficult than the first. If you have damaged cartilage in your knee, you should protect that knee for the rest of your life. Running, fast walking and jumping cause further damage, while pedaling and swimming usually do not. When the knee hurts all the time, your doctor will check to see how much cartilage is left. If it's gone, you probably need a knee replacement. See my reports on Synvisc injections into knees and arthroscopic knee surgery.