X-rays Tell the Story
X-rays can show mild osteoarthritis while you may be experiencing severe symptoms. The reverse is also true -- an x-ray may show changes that point to advanced osteoarthritis while you may be experiencing few, if any, symptoms. Even though early cartilage abnormalities are detectable with magnetic resonance imaging (MRIs), usually x-rays are ordered initially to help diagnose osteoarthritis.
Joint Space Narrowing
If the joint damage that appears on x-ray is severe, you may be told that you are "bone-on-bone." Bone-on-bone is a layman's term that refers to complete joint space narrowing, which is the result of cartilage loss.
As cartilage deteriorates, there is less cushioning between the ends of the bone that form the joint. The space between the ends of the bone decreases, and the ends of the bone become closer to each other. When there is essentially no cartilage left, the bones rub against each other. The term bone-on-bone refers to the ends of the bones rubbing against each other.
A Disease of the Cartilage
Osteoarthritis is primarily considered a disease of cartilage. As cartilage wears away, the role it serves as a shock absorber and lubricant (to protect the ends of the bones and allow friction-free movement) is affected. Healthy cartilage works in harmony with bones, muscles, tendons, ligaments, and other support structures to maintain joint function and mobility.
When a joint is at an advanced stage of osteoarthritis and has become bone-on-bone, range of motion can be very limited and it is typically very painful.
All About Osteoarthritis. Nancy E. Lane, M.D. and Daniel J. Wallace., M.D., Oxford University Press, 2002