National Institute of Arthritis and Musculoskeletal and Skin Diseases
What Is Osteoarthritis?
Osteoarthritis (AH-stee-oh-ar-THREYE-tis) is the most common
type of arthritis, and is seen especially among older people. Sometimes it is
called degenerative joint disease or osteoarthrosis.
Osteoarthritis mostly affects cartilage (KAR-til-uj), the hard
but slippery tissue that covers the ends of bones where they meet to form a
joint. Healthy cartilage allows bones to glide over one another. It also
absorbs energy from the shock of physical movement. In osteoarthritis, the
surface layer of cartilage breaks down and wears away. This allows bones under
the cartilage to rub together, causing pain, swelling, and loss of motion of
the joint. Over time, the joint may lose its normal shape. Also, small deposits
of bone – called osteophytes or bone spurs – may grow on the edges of the
joint. Bits of bone or cartilage can break off and float inside the joint
space. This causes more pain and damage.
People with osteoarthritis usually have joint pain and some
movement limitations. Unlike some other forms of arthritis, such as rheumatoid
arthritis, osteoarthritis affects only joint function and does not affect skin
tissue, the lungs, the eyes, or the blood vessels.
In rheumatoid arthritis, the second most common form of
arthritis, the immune system attacks the tissues of the joints, leading to
pain, inflammation, and eventually joint damage and malformation. It typically
begins at a younger age than osteoarthritis, causes swelling and redness in
joints, and may make people feel sick, tired, and uncommonly feverish.
Who Has Osteoarthritis?
Osteoarthritis is by far the most common type of arthritis, and
the percentage of people who have it grows higher with age. An estimated 12.1
percent of the U.S. population (nearly 21 million Americans) age 25 and older
Although osteoarthritis is more common in older people, younger
people can develop it – usually as the result of a joint injury, a joint
malformation, or a genetic defect in joint cartilage. Both men and women have
the disease. Before age 45, more men than women have osteoarthritis; after age
45, it is more common in women. It is also more likely to occur in people who
are overweight and in those with jobs that stress particular joints.
As the population ages, the number of people with
osteoarthritis will only grow. By 2030, 20 percent of Americans – about 72
million people – will have passed their 65th birthday and will be at high risk
for the disease.