Why it's done

Slick cartilage covers the ends of the bones in a healthy knee and this allows the bones to move smoothly against each other. Osteoarthritis damages and wears away the cartilage — creating a rough surface.

When the cartilage wears unevenly, it narrows the space between the femur and tibia, causing the knee to bow inward or outward, depending on which side of the knee is affected. Removing or adding a wedge of bone in your upper shinbone or lower thighbone can help straighten the bowing, shift your weight to the undamaged part of your knee joint and prolong the life span of the knee joint.