Arthritis is a disease where you lose cartilage and then you progressively lose bone, and then you progressively stretch out ligaments, in that order. So, if you have arthritis on the inner side of your knee, which is the most common pattern, as the cartilage wears out, the bones go into a bow-legged position, and then, that bone wears, then you actually start to lose bone, and then eventually you actually start to stretch out the tissues on the outside of the knee just from tension, and then they become unstable. People feel the knees are wobbly or they’re afraid to go down a flight of steps normally or carry their laundry down a flight of steps. Or older people will fall.

Boomers mean big business in joint replacement | BetterLiving.com.