Osteoarthritis of the knee may keep you from being as active as you like. And it may come from a gradual breakdown of your knee’s cartilage. That’s a protective tissue on the ends of your bones. In a healthy knee, the bones glide smoothly against each other. But in a knee with osteoarthritis, cartilage begins to wear away. Bone rubs against bone. Bony bumps we call “bone spurs” may form.