Slick cartilage allows the ends of the bones in a healthy knee to move smoothly against each other. In osteoarthritis, this cartilage is damaged and worn away — creating a rough surface.

The lower portion of the thighbone has two knobs that move against the flatter surface of the top of the shinbone. If arthritis damage affects only one of these knobs, it can make your knee uneven — causing it to bow inward or outward. Removing or adding a wedge of bone in your upper shinbone or lower thighbone can help straighten out this bowing and shift your weight to the undamaged part of your knee joint.

Aug. 23, 2011